NORMAL GENOMIC

• McKay SL, Johnson TL
• An Investigation of a Role for U2 snRNP Spliceosomal Components inRegulating Transcription.
• PLoS One. 2011; 6: 16077-16077
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• There is mounting evidence to suggest that the synthesis of pre-mRNAtranscripts and their subsequent splicing are coordinated events. Previousstudies have implicated the mammalian spliceosomal U2 snRNP as having anovel role in stimulating transcriptional elongation in vitro throughinteractions with the elongation factors P-TEFb and Tat-SF1; however, themechanism remains unknown [1]. These factors are conserved inSaccharomyces cerevisiae, a fact that suggests that a similar interactionmay occur in yeast to stimulate transcriptional elongation in vivo. Toaddress this possibility we have looked for evidence of a role for theyeast Tat-SF1 homolog, Cus2, and the U2 snRNA in regulating transcription.Specifically, we have performed a genetic analysis to look for functionalinteractions between Cus2 or U2 snRNA and the P-TEFb yeast homologs, theBur1/2 and Ctk1/2/3 complexes. In addition, we have analyzed Cus2-deletedor -overexpressing cells and U2 snRNA mutant cells to determine if theyshow transcription-related phenotypes similar to those displayed by theP-TEFb homolog mutants. In no case have we been able to observe phenotypesconsistent with a role for either spliceosomal factor in transcriptionelongation. Furthermore, we did not find evidence for physicalinteractions between the yeast U2 snRNP factors and the P-TEFb homologs.These results suggest that in vivo, S. cerevisiae do not exhibitfunctional or physical interactions similar to those exhibited by theirmammalian counterparts in vitro. The significance of the differencebetween our in vivo findings and the previously published in vitro resultsremains unclear; however, we discuss the potential importance of otherfactors, including viral proteins, in mediating the mammalianinteractions.

• Balakrishnan SK, Gross DS
• The tumor suppressor p53 associates with gene coding regions andco-traverses with elongating RNA polymerase II in an in vivo model.
• Oncogene. 2008; 27: 2661-72
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• Sequence-specific transcriptional regulators function by stably bindingcognate DNA sequences followed by recruitment of both general andspecialized factors to target gene promoters. The tumor suppressor p53mediates its anti-oncogenic effect on cells by functioning as asequence-specific regulator. p53 employs a secondary mechanism to suppresstumor formation by permeabilizing the outer mitochondrial membrane,thereby releasing pro-apoptotic factors. Here, we report a potential thirdbiological function of p53: as a transcriptional elongation factor. Usingchromatin immunoprecipitation, we demonstrate that human p53 robustlyassociates with RNA polymerase II (Pol II), but neither Pol I- nor PolIII-transcribed regions in the budding yeast, Saccharomyces cerevisiae.p53's association with open reading frames is mediated by its physicalinteraction with elongating Pol II, with which p53 travels in vivo andco-immunoprecipitates in vitro. When similarly expressed, the potentacidic activator VP16 cannot be cross-linked to Pol II coding regions. p53levels comparable to those found in induced mammalian cells confersynthetic sickness or lethality in combination with deletions in genesencoding transcription elongation factors; p53 likewise confershypersensitivity to the anti-elongation drug 6-azauracil. Collectively,our results indicate that p53 can physically interact with thetranscription elongation complex and influence transcription elongation,and open up new avenues of investigation in mammalian cells.

• Bennett CB et al.
• Yeast screens identify the RNA polymerase II CTD and SPT5 as relevanttargets of BRCA1 interaction.
• PLoS One. 2008; 3: 1448-1448
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• BRCA1 has been implicated in numerous DNA repair pathways that maintaingenome integrity, however the function responsible for its tumorsuppressor activity in breast cancer remains obscure. To identify the mosthighly conserved of the many BRCA1 functions, we screened theevolutionarily distant eukaryote Saccharomyces cerevisiae for mutants thatsuppressed the G1 checkpoint arrest and lethality induced followingheterologous BRCA1 expression. A genome-wide screen in the diploiddeletion collection combined with a screen of ionizing radiation sensitivegene deletions identified mutants that permit growth in the presence ofBRCA1. These genes delineate a metabolic mRNA pathway that temporallylinks transcription elongation (SPT4, SPT5, CTK1, DEF1) tonucleopore-mediated mRNA export (ASM4, MLP1, MLP2, NUP2, NUP53, NUP120,NUP133, NUP170, NUP188, POM34) and cytoplasmic mRNA decay at P-bodies(CCR4, DHH1). Strikingly, BRCA1 interacted with the phosphorylated RNApolymerase II (RNAPII) carboxy terminal domain (P-CTD), phosphorylated inthe pattern specified by the CTDK-I kinase, to induce DEF1-dependentcleavage and accumulation of a RNAPII fragment containing the P-CTD.Significantly, breast cancer associated BRCT domain defects in BRCA1 thatsuppressed P-CTD cleavage and lethality in yeast also suppressed thephysical interaction of BRCA1 with human SPT5 in breast epithelial cells,thus confirming SPT5 as a relevant target of BRCA1 interaction.Furthermore, enhanced P-CTD cleavage was observed in both yeast and humanbreast cells following UV-irradiation indicating a conserved eukaryoticdamage response. Moreover, P-CTD cleavage in breast epithelial cells wasBRCA1-dependent since damage-induced P-CTD cleavage was only observed inthe mutant BRCA1 cell line HCC1937 following ectopic expression of wildtype BRCA1. Finally, BRCA1, SPT5 and hyperphosphorylated RPB1 form acomplex that was rapidly degraded following MMS treatment in wild type butnot BRCA1 mutant breast cells. These results extend the mechanistic linksbetween BRCA1 and transcriptional consequences in response to DNA damageand suggest an important role for RNAPII P-CTD cleavage in BRCA1-mediatedcancer suppression.

• Guglielmi B, Soutourina J, Esnault C, Werner M
• TFIIS elongation factor and Mediator act in conjunction duringtranscription initiation in vivo.
• Proc Natl Acad Sci U S A. 2007; 104: 16062-7
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• The transcription initiation and elongation steps of protein-coding genesusually rely on unrelated protein complexes. However, the TFIIS elongationfactor is implicated in both processes. We found that, in the absence ofthe Med31 Mediator subunit, yeast cells required the TFIIS polymerase II(Pol II)-binding domain but not its RNA cleavage stimulatory activity thatis associated with its elongation function. We also found that the TFIISPol II-interacting domain was needed for the full recruitment of Pol II toseveral promoters in the absence of Med31. This work demonstrated that, inaddition to its thoroughly characterized role in transcription elongation,TFIIS is implicated through its Pol II-binding domain in the formation orstabilization of the transcription initiation complex in vivo.

• Weltmeier F et al.
• Combinatorial control of Arabidopsis proline dehydrogenase transcriptionby specific heterodimerisation of bZIP transcription factors.
• EMBO J. 2006; 25: 3133-43
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• Proline metabolism has been implicated in plant responses to abioticstresses. The Arabidopsis thaliana proline dehydrogenase (ProDH) iscatalysing the first step in proline degradation. Transcriptionalactivation of ProDH by hypo-osmolarity is mediated by an ACTCAT ciselement, a typical binding site of basic leucine zipper (bZIP)transcription factors. In this study, we demonstrate by gain-of-functionand loss-of-function approaches, as well as chromatin immunoprecipitation(ChIP), that ProDH is a direct target gene of the group-S bZIP factorAtbZIP53. Dimerisation studies making use of yeast and Arabidopsisprotoplast-based two-hybrid systems, as well as bimolecular fluorescencecomplementation (BiFC) reveal that AtbZIP53 does not preferentially formdimers with group-S bZIPs but strongly interacts with members of group-C.In particular, a synergistic interplay of AtbZIP53 and group-C AtbZIP10was demonstrated by colocalisation studies, strong enhancement ofACTCAT-mediated transcription as well as complementation studies inatbzip53 atbzip10 T-DNA insertion lines. Heterodimer mediated activationof transcription has been found to operate independent of the DNA-bindingproperties and is described as a crucial mechanism to modulatetranscription factor activity and function.

• Xiao T et al.
• Histone H2B ubiquitylation is associated with elongating RNA polymeraseII.
• Mol Cell Biol. 2005; 25: 637-51
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• Rad6-mediated ubiquitylation of histone H2B at lysine 123 has been linkedto transcriptional activation and the regulation of lysine methylation onhistone H3. However, how Rad6 and H2B ubiquitylation contribute to thetranscription and histone methylation processes is poorly understood.Here, we show that the Paf1 transcription elongation complex and the E3ligase for Rad6, Bre1, mediate an association of Rad6 with thehyperphosphorylated (elongating) form of RNA polymerase II (Pol II). Thisassociation appears to be necessary for the transcriptional activities ofRad6, as deletion of various Paf1 complex members or Bre1 abolishes H2Bubiquitylation (ubH2B) and reduces the recruitment of Rad6 to thepromoters and transcribed regions of active genes. Using the inducibleGAL1 gene as a model, we find that the recruitment of Rad6 upon activationoccurs rapidly and transiently across the gene and coincides preciselywith the appearance of Pol II. Significantly, during GAL1 activation in anrtf1 deletion mutant, Rad6 accumulates at the promoter but is absent fromthe transcribed region. This fact suggests that Rad6 is recruited topromoters independently of the Paf1 complex but then requires this complexfor entrance into the coding region of genes in a Pol II-associatedmanner. In support of a role for Rad6-dependent H2B ubiquitylation intranscription elongation, we find that ubH2B levels are dramaticallyreduced in strains bearing mutations of the Pol II C-terminal domain (CTD)and abolished by inactivation of Kin28, the serine 5 CTD kinase thatpromotes the transition from initiation to elongation. Furthermore,synthetic genetic array analysis reveals that the Rad6 complex interactsgenetically with a number of known or suspected transcription elongationfactors. Finally, we show that Saccharomyces cerevisiae mutants bearingdefects in the pathway to H2B ubiquitylation display transcriptionelongation defects as assayed by 6-azauracil sensitivity. Collectively,our results indicate a role for Rad6 and H2B ubiquitylation during theelongation cycle of transcription and suggest a mechanism by which H3methylation may be regulated.

• Wilcox CB, Rossettini A, Hanes SD
• Genetic interactions with C-terminal domain (CTD) kinases and the CTD ofRNA Pol II suggest a role for ESS1 in transcription initiation andelongation in Saccharomyces cerevisiae.
• Genetics. 2004; 167: 93-105
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• Ess1 is an essential prolyl isomerase that binds the C-terminal domain(CTD) of Rpb1, the large subunit of RNA polymerase II. Ess1 is proposed tocontrol transcription by isomerizing phospho-Ser-Pro peptide bonds withinthe CTD repeat. To determine which step(s) in the transcription cyclemight require Ess1, we examined genetic interactions between ESS1 andgenes encoding the known CTD kinases (KIN28, CTK1, BUR1, and SRB10).Although genetic interactions were identified between ESS1 and all fourkinases, the clearest interactions were with CTK1 and SRB10. Reduceddosage of CTK1 rescued the growth defect of ess1(ts) mutants, whileoverexpression of CTK1 enhanced the growth defects of ess1(ts) mutants.Deletion of SRB10 suppressed ess1(ts) and ess1Delta mutants. Theinteractions suggest that Ess1 opposes the functions of these kinases,which are thought to function in preinitiation and elongation. Using aseries of CTD substitution alleles, we also identified Ser5-Pro6 as apotential target for Ess1 isomerization within the first "half" of the CTDrepeats. On the basis of the results, we suggest a model in whichEss1-directed conformational changes promote dephosphorylation of Ser5 tostimulate preinitiation complex formation and, later, to inhibitelongation.

• Mitton KP, Swain PK, Khanna H, Dowd M, Apel IJ, Swaroop A
• Interaction of retinal bZIP transcription factor NRL with Flt3-interactingzinc-finger protein Fiz1: possible role of Fiz1 as a transcriptionalrepressor.
• Hum Mol Genet. 2003; 12: 365-73
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• NRL (neural retina leucine zipper) is a basic motif leucine zippertranscription factor of the Maf-subfamily. Multiple phosphorylatedisoforms of NRL are detected specifically in rod photoreceptors. NRLregulates the expression of several rod-specific genes, includingrhodopsin and cGMP phosphodiesterase beta-subunit, in synergy with othertranscription factors (e.g. the homeodomain protein CRX). Missensemutations in the human NRL gene are associated with autosomal dominantretinitis pigmentosa, whereas the loss of its function leads to rodlessretina in Nrl-knockout mice that exhibit enhanced S-cone function. Tofurther elucidate the molecular mechanism(s) underlying NRL-mediatedtranscriptional regulation, we used yeast two-hybrid screening to isolateNRL-interacting proteins in the retina and report the identification ofFlt3-interacting zinc-finger protein, Fiz1. Interaction of Fiz1 andNRL-leucine zipper was validated by GST pulldown assays andco-immunoprecipitation from bovine retinal nuclear extracts. Fiz1suppressed NRL- but not CRX-mediated transactivation of rhodopsin promoteractivity in transiently transfected CV1 cells. The mRNA and the proteinfor both Fiz1 and its only other known interacting protein Flt3, areceptor tyrosine kinase, are expressed in the retina. Our resultsindicate potential cross-talk among signaling pathways in the retina andsuggest that the function of NRL is modulated by its interaction withspecific repressor proteins.

• Schiermeyer A, Thurow C, Gatz C
• Tobacco bZIP factor TGA10 is a novel member of the TGA family oftranscription factors.
• Plant Mol Biol. 2003; 51: 817-29
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• TGA factors constitute a family of conserved plant bZ1P transcriptionfactors that regulate transcription from as-1-like elements in response toplant signalling molecules salicylic acid (SA), methyl jasmonate (MJ) andauxin. Based on sequence similarities, two subclasses of TGA factors havebeen identified before in tobacco: class I factors (TGA1a and PG13) arepreferentially expressed in root tip meristems, whereas class II factors(TGA2.1 and TGA2.2) are found in leaves and in roots. Here we describe anovel member of the tobacco TGA family (TGA10), which defines a distinctsubclass of its own. TGA10 mRNA and TGA10 protein were found in roots butnot in leaves of mature tobacco plants. TGA10 binds specifically to theas-1 element, interacts with TGA2.2, and activates transcription in yeast.When ectopically expressed in leaves, TGA10 enhanced SA-, auxin- andMJ-inducibility of target gene Nt103, which responds in the same manner toenhanced levels of TGA2.2. This indicates that TGA10, albeit normally notpresent in leaves, can interact with the leaf regulatory networkcontrolling transcription from as-1-containing promoters. However, Nt103expression was not affected in roots of TGA10-over-expressing plants,implying the existence of root-specific mechanisms which do not allow apositive effect of increased TGA10 levels on target gene expression.

• Qi H et al.
• AIbZIP, a novel bZIP gene located on chromosome 1q21.3 that is highlyexpressed in prostate tumors and of which the expression is up-regulatedby androgens in LNCaP human prostate cancer cells.
• Cancer Res. 2002; 62: 721-33
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• Androgens play an important role in the development and physiology of thenormal prostate as well as in prostate cancer cell proliferation.Comparison of the mRNA expression profiles of control and R1881-treatedcultures of LNCaP human prostate cancer cells using cDNA subtraction ledto the identification of a novel transcription factor that we namedAndrogen-Induced bZIP (AIbZIP) protein. AIbZIP is a 395 aa protein withhomology to cyclic AMP-responsive element binding protein/activatingtranscription factor transcription factors. It contains an NH(2)-terminalactivation domain, a central bZIP domain, and a COOH-terminaltransmembrane domain. The AIbZIP gene is localized on chromosome 1q21.3and consists of 10 exons. A major 1.7-kb transcript was detectedexclusively in the prostate as well as in breast and prostate cancer celllines. Androgens up-regulate AIbZIP mRNA and protein levels in adose-dependent manner. The kinetics of AIbZIP mRNA up-regulation and theresults of experiments with cycloheximide suggest that AIbZIP may be adelayed response gene. Immunoreactive AIbZIP protein was primarilydetected in the cytoplasm of prostatic luminal epithelial cells.Similarly, full-length AIbZIP-green fluorescent protein fusion proteinswere localized in the cytoplasm of LNCaP cells, whereas a truncated formof AIbZIP lacking the putative transmembrane domain was exclusivelynuclear. Examination of AIbZIP protein and mRNA expression in a series oftransurethral resection of the prostate and needle biopsy specimensindicated that AIbZIP is expressed at higher levels in cancerous prostatecells compared with noncancerous prostate cells. The highlytissue-specific expression profile, androgen regulation, chromosomallocalization, and expression profile of AIbZIP in prostate tumors suggestthat AIbZIP may play an important role in prostate cancer and in androgenreceptor signaling in prostate cells. Future studies will confirm apossible relationship between AIbZIP and prostate cancer.

• Brewster NK, Johnston GC, Singer RA
• A bipartite yeast SSRP1 analog comprised of Pob3 and Nhp6 proteinsmodulates transcription.
• Mol Cell Biol. 2001; 21: 3491-502
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• The FACT complex of vertebrate cells, comprising the Cdc68 (Spt16) andSSRP1 proteins, facilitates transcription elongation on a nucleosomaltemplate and modulates the elongation-inhibitory effects of the DSIFcomplex in vitro. Genetic findings show that the related yeast(Saccharomyces cerevisiae) complex, termed CP, also mediatestranscription. The CP components Cdc68 and Pob3 closely resemble the FACTcomponents, except that the C-terminal high-mobility group (HMG) boxdomain of SSRP1 is not found in the yeast homolog Pob3. We show here thatNhp6a and Nhp6b, small HMG box proteins with overlapping functions inyeast, associate with the CP complex and mediate CP-related geneticeffects on transcription. Absence of the Nhp6 proteins causes severeimpairment in combination with mutations impairing the Swi-Snfchromatin-remodeling complex and the DSIF (Spt4 plus Spt5) elongationregulator, and sensitizes cells to 6-azauracil, characteristic ofelongation effects. An artificial SSRP1-like protein, created by fusingthe Pob3 and Nhp6a proteins, provides both Pob3 and Nhp6a functions fortranscription, and competition experiments indicate that these functionsare exerted in association with Cdc68. This particular Pob3-Nhp6a fusionprotein was limited for certain Nhp6 activities, indicating that its Nhp6afunction is compromised. These findings suggest that in yeast cells theCdc68 partners may be both Pob3 and Nhp6, functioning as a bipartiteanalog of the vertebrate SSRP1 protein.

• Gallardo M, Aguilera A
• A new hyperrecombination mutation identifies a novel yeast gene, THP1,connecting transcription elongation with mitotic recombination.
• Genetics. 2001; 157: 79-89
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• Given the importance of the incidence of recombination in genomicinstability, it is of great interest to know the elements or processescontrolling recombination in mitosis. One such process is transcription,which has been shown to induce recombination in bacteria, yeast, andmammals. To further investigate the genetic control of the incidence ofrecombination and genetic instability and, in particular, its connectionwith transcription, we have undertaken a search for hyperrecombinationmutants among a large number of strains deleted in genes of unknownfunction. We have identified a new gene, THP1 (YOL072w), whose deletionmutation strongly stimulates recombination between repeats. In addition,thp1 Delta impairs transcription, a defect that is particularly strong atthe level of elongation through particular DNA sequences such as lacZ. Thehyperrecombination phenotype of thp1 Delta cells is fully dependent ontranscription elongation of the repeat construct. When transcription isimpeded either by shutting off the promoter or by using a prematuretranscription terminator, hyperrecombination between repeats is abolished,providing new evidence that transcription-elongation impairment may be asource of recombinogenic substrates in mitosis. We show that Thp1p and twoother proteins previously shown to control transcription-associatedrecombination, Hpr1p and Tho2p, act in the same "pathway" connectingtranscription elongation with the incidence of mitotic recombination.

• Lemaire M, Collart MA
• The TATA-binding protein-associated factor yTafII19p functionallyinteracts with components of the global transcriptional regulator Ccr4-Notcomplex and physically interacts with the Not5 subunit.
• J Biol Chem. 2000; 275: 26925-34
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• The Saccharomyces cerevisiae HIS3 gene is a model system to characterizetranscription initiation from different types of core promoters. The NOTgenes were identified by mutations that preferentially increasedtranscription of the HIS3 promoter lacking a canonical TATA sequence. Theyencode proteins associated in a complex that also contains the Caf1 andCcr4 proteins. It has been suggested that the Ccr4-Not complex repressestranscription by inhibiting factors more specifically required forpromoters lacking a TATA sequence. A potential target is the yTaf(II)19subunit of TFIID, which, when depleted, leads to a preferential decreaseof HIS3 TATA-less transcription. We isolated conditional taf19 allelesthat display synthetic growth phenotypes when combined with not4 orspecific not5 alleles. Inactivation of yTaf(II)19p by shifting thesemutants to the restrictive temperature led to a more rapid and strikingdecrease in transcription from promoters that do not contain a canonicalTATA sequence. We demonstrated by the two-hybrid assay and directly invitro that yTaf(II)19p and Not5p could interact. Finally, we found by thetwo-hybrid assay that yTaf(II)19p also interacted with many components ofthe Ccr4-Not complex. Taken together, our results provide evidence thatinteractions between Not5p and yTaf(II)19p may be involved intranscriptional regulation by the Ccr4-Not complex.

• Bharti K, Schmidt E, Lyck R, Heerklotz D, Bublak D, Scharf KD
• Isolation and characterization of HsfA3, a new heat stress transcriptionfactor of Lycopersicon peruvianum.
• Plant J. 2000; 22: 355-65
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• Stress-induced transcription of heat shock proteins (Hsps) in eukaryotesis mediated by a conserved class of transcription factors called heatstress transcription factors (Hsfs). Here we report the isolation andfunctional characterization of HsfA3, a new member of the Hsf family.HsfA3 was cloned from a tomato heat stress cDNA library by yeasttwo-hybrid screening, using HsfA1 as a bait. HsfA3 is a single-copy genewith all the conserved sequence elements characteristic of a heat stresstranscription factor. The constitutively expressed HsfA3 is mainly foundin the cytoplasm under control conditions and in the nucleus under heatstress conditions. Functionally, HsfA3 behaves similarly to the alreadyknown members of tomato Hsf family. It is able to substitute yeast Hsf forviability functions and is a strong activator of Hsf-dependent reporterconstructs both in tobacco protoplasts and yeast. Finally, similar to theAHA motifs in HsfA1 and HsfA2, the activator function depends on fourshort peptide motifs with a central tryptophan residue found in theC-terminal domain of HsfA3.

• Pappas DL Jr, Hampsey M
• Functional interaction between Ssu72 and the Rpb2 subunit of RNApolymerase II in Saccharomyces cerevisiae.
• Mol Cell Biol. 2000; 20: 8343-51
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• SSU72 is an essential gene encoding a phylogenetically conserved proteinof unknown function that interacts with the general transcription factorTFIIB. A recessive ssu72-1 allele was identified as a synthetic enhancerof a TFIIB (sua7-1) defect, resulting in a heat-sensitive (Ts(-))phenotype and a dramatic downstream shift in transcription start siteselection. Here we describe a new allele, ssu72-2, that confers a Ts(-)phenotype in a SUA7 wild-type background. In an effort to further defineSsu72, we isolated suppressors of the ssu72-2 mutation. One suppressor isallelic to RPB2, the gene encoding the second-largest subunit of RNApolymerase II (RNAP II). Sequence analysis of the rpb2-100 suppressordefined a cysteine replacement of the phylogenetically invariant arginineresidue at position 512 (R512C), located within homology block D of Rpb2.The ssu72-2 and rpb2-100 mutations adversely affected noninduced geneexpression, with no apparent effects on activated transcription in vivo.Although isolated as a suppressor of the ssu72-2 Ts(-) defect, rpb2-100enhanced the transcriptional defects associated with ssu72-2. The Ssu72protein interacts directly with purified RNAP II in acoimmunoprecipitation assay, suggesting that the genetic interactionsbetween ssu72-2 and rpb2-100 are a consequence of physical interactions.These results define Ssu72 as a highly conserved factor that physicallyand functionally interacts with the RNAP II core machinery duringtranscription initiation.

• Moriya H, Isono K
• Analysis of genetic interactions between DHH1, SSD1 and ELM1 indicatestheir involvement in cellular morphology determination in Saccharomycescerevisiae.
• Yeast. 1999; 15: 481-96
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• The DHH1 gene of Saccharomyces cerevisiae belongs to a family of genesthat encode highly conserved DEAD-box proteins commonly present in variouseukaryotic organisms. Its precise function in yeast has not yet been welldocumented. To investigate its role in vivo, we constructed a DHH1disruptant, characterized it genetically and searched for genes themutations in which would cause synthetic lethality in combination with theDHH1 disruption. CDC28, ELM1 and SSD1 were thus found to be suchcandidates and we subsequently analysed their interactions. Mutations inELM1 were previously reported to result in the elongation of cells. Weconfirmed this phenotype and observed in addition elongated bud formationin an Elm1p overproducing strain. Also, Elm1p fused with the greenfluorescent protein (GFP) was found to be localized at the bud neck. Theseand other observations seem to suggest that Elm1p plays a role duringcytokinesis in S. cerevisiae. The phenotypes of strains harbouring eitherdelta dhh1 delta elm1 or ssd1-d delta elm1 were very similar to eachother, showing abnormal cellular morphology and defects in cytokinesis andmitosis. Furthermore, DHH1 and SSD1 could functionally complement eachother in the ade2 red colour pigment formation, hypersensitivity to SDS,growth on synthetic media and at high temperature. A triple mutant, deltadhh1 ssd1-d delta elm1, apparently had very fragile cell walls and couldgrow only in a medium supplemented with 1 M sorbitol.

• Paranjape SM, Kamakaka RT, Kadonaga JT
• Role of chromatin structure in the regulation of transcription by RNApolymerase II.
• Annu Rev Biochem. 1994; 63: 265-97

• Ramachandran S, Hiratsuka K, Chua NH
• Transcription factors in plant growth and development.
• Curr Opin Genet Dev. 1994; 4: 642-6
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• The target DNA sequences of several classes of plant transcriptionfactors, including basic leucine zipper (bZIP) proteins and Myb-relatedfactors, have been characterized in vivo as well as in vitro. The bZIPproteins, for example, act at ACGT elements, the flanking nucleotidesdetermining their binding specificities. Overexpression, co-suppression,and antisense technology studies of factor genes in transgenic plants haveuncovered the roles of bZIP, homeodomain, and MADS box factors in plantgrowth and development; for example, ectopic expression of pMADS1 alone inearly Petunia development is sufficient for homeotic conversion of sepalsinto petaloid organs.

• McCarty DR, Hattori T, Carson CB, Vasil V, Lazar M, Vasil IK
• The Viviparous-1 developmental gene of maize encodes a noveltranscriptional activator.
• Cell. 1991; 66: 895-905
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• The Viviparous-1 (Vp1) gene of maize is specifically required forexpression of the maturation program in seed development. We show that Vp1encodes a 73,335 dalton protein with no detectable homology to knownproteins. An acidic transcriptional activation sequence was identified byfusion to the GAL4 DNA-binding domain. Expression of VP1 in maizeprotoplasts resulted in strong activation (greater than 130-fold) of areporter gene fused to the promoter of a presumptive target gene. Theacidic domain in VP1 was essential for transactivation and could befunctionally replaced by the activator sequence of the herpes simplexvirus VP16 protein. Our results indicate that VP1 is a novel transcriptionfactor possibly involved in potentiation of a seed-specific hormoneresponse.