NORMAL GENOMIC

• Shimasaki NB, Kane CM
• Structural basis for the species-specific activity of TFIIS.
• J Biol Chem. 2000; 275: 36541-9
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• Many proteins involved in eukaryotic transcription are similar in function and in sequence between organisms. Despite the sequence similarities, there are many factors that do not function across species. For example, transcript elongation factor TFIIS is highly conserved among eukaryotes, and yet the TFIIS protein from Saccharomyces cerevisiae cannot function with mammalian RNA polymerase II and vice versa. To determine the reason for this species specificity, chimeras were constructed linking three structurally independent regions of the TFIIS proteins from yeast and human cells. Two independently folding domains, II and III, have been examined previously using NMR (). Yeast domain II alone is able to bind yeast RNA polymerase II with the same affinity as the full-length TFIIS protein, and this domain was expected to confer the species selectivity. Domain III has previously been shown to be readily exchanged between mammalian and yeast factors. However, the results presented here indicate that domain II is insufficient to confer species selectivity, and a primary determinant lies in a 30-amino acid highly conserved linker region connecting domain II with domain III. These 30 amino acids may physically orient domains II and III to support functional interactions between TFIIS and RNA polymerase II.

• Okuda M, Watanabe Y, Okamura H, Hanaoka F, Ohkuma Y, Nishimura Y
• Structure of the central core domain of TFIIEbeta with a novel double-stranded DNA-binding surface.
• EMBO J. 2000; 19: 1346-56
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• Human general transcription factor TFIIE consists of two subunits, TFIIEalpha and TFIIEbeta. Recently, TFIIEbeta has been found to bind to the region where the promoter starts to open to be single-stranded upon transcription initiation by RNA polymerase II. Here, the central core domain of human TFIIEbeta (TFIIEbetac) has been identified by a limited proteolysis. This solution structure has been determined by NMR. It consists of three helices with a beta hairpin at the C-terminus, resembling the winged helix proteins. However, TFIIEbetac shows a novel double-stranded DNA-binding activity where the DNA-binding surface locates on the opposite side to the previously reported winged helix motif by forming a positively charged furrow. A model will be proposed that TFIIE stabilizes the preinitiation complex by binding not only to the general transcription factors together with RNA polymerase II but also to the promoter DNA, where double-stranded DNA starts to open to be single-stranded upon activation of the preinitiation complex.

• Hemming SA, Edwards AM
• Yeast RNA polymerase II subunit RPB9. Mapping of domains required for transcription elongation.
• J Biol Chem. 2000; 275: 2288-94
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• The RPB9 subunit of RNA polymerase II regulates transcription elongation activity and is required for the action of the transcription elongation factor, TFIIS. RPB9 comprises two zinc ribbon domains joined by a conserved linker region. The C-terminal zinc ribbon is similar in sequence to that found in TFIIS. To elucidate the relationship between the structure and transcription elongation function of RPB9, we initiated a mutagenesis study on the Saccharomyces cerevisiae homologue. The individual zinc ribbon domains, in isolation or in combination, could not stimulate transcription by a polymerase lacking RPB9, pol IIDelta9. Mutations in the N-terminal zinc ribbon had little effect on transcription activity. By contrast, mutations in the acidic loop that connects the second and third beta-strands of the C-terminal zinc ribbon were completely inactive for transcription. Interestingly, the analogous residues in TFIIS are also critical for elongation activity. A conserved charged stretch in the linker region (residues 89-95, DPTLPR) mediated the interaction with RNA polymerase II.

• Cramer P et al.
• Architecture of RNA polymerase II and implications for the transcription mechanism.
• Science. 2000; 288: 640-9
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• A backbone model of a 10-subunit yeast RNA polymerase II has been derived from x-ray diffraction data extending to 3 angstroms resolution. All 10 subunits exhibit a high degree of identity with the corresponding human proteins, and 9 of the 10 subunits are conserved among the three eukaryotic RNA polymerases I, II, and III. Notable features of the model include a pair of jaws, formed by subunits Rpb1, Rpb5, and Rpb9, that appear to grip DNA downstream of the active center. A clamp on the DNA nearer the active center, formed by Rpb1, Rpb2, and Rpb6, may be locked in the closed position by RNA, accounting for the great stability of transcribing complexes. A pore in the protein complex beneath the active center may allow entry of substrates for polymerization and exit of the transcript during proofreading and passage through pause sites in the DNA.

• Tan Q, Linask KL, Ebright RH, Woychik NA
• Activation mutants in yeast RNA polymerase II subunit RPB3 provide evidence for a structurally conserved surface required for activation in eukaryotes and bacteria.
• Genes Dev. 2000; 14: 339-48
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• We have identified a mutant in RPB3, the third-largest subunit of yeast RNA polymerase II, that is defective in activator-dependent transcription, but not defective in activator-independent, basal transcription. The mutant contains two amino-acid substitutions, C92R and A159G, that are both required for pronounced defects in activator-dependent transcription. Synthetic enhancement of phenotypes of C92R and A159G, and of several other pairs of substitutions, is consistent with a functional relationship between residues 92-95 and 159-161. Homology modeling of RPB3 on the basis of the crystallographic structure of alphaNTD indicates that residues 92-95 and 159-162 are likely to be adjacent within the structure of RPB3. In addition, homology modeling indicates that the location of residues 159-162 within RPB3 corresponds to the location of an activation target within alphaNTD (the target of activating region 2 of catabolite activator protein, an activation target involved in a protein-protein interaction that facilitates isomerization of the RNA polymerase promoter closed complex to the RNA polymerase promoter open complex). The apparent finding of a conserved surface required for activation in eukaryotes and bacteria raises the possibility of conserved mechanisms of activation in eukaryotes and bacteria.

• Ishiguro A, Nogi Y, Hisatake K, Muramatsu M, Ishihama A
• The Rpb6 subunit of fission yeast RNA polymerase II is a contact target of the transcription elongation factor TFIIS.
• Mol Cell Biol. 2000; 20: 1263-70
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• The Rpb6 subunit of RNA polymerase II is one of the five subunits common to three forms of eukaryotic RNA polymerase. Deletion and truncation analyses of the rpb6 gene in the fission yeast Schizosaccharomyces pombe indicated that Rpb6, consisting of 142 amino acid residues, is an essential protein for cell viability, and the essential region is located in the C-terminal half between residues 61 and 139. After random mutagenesis, a total of 14 temperature-sensitive mutants were isolated, each carrying a single (or double in three cases and triple in one) mutation. Four mutants each carrying a single mutation in the essential region were sensitive to 6-azauracil (6AU), which inhibits transcription elongation by depleting the intracellular pool of GTP and UTP. Both 6AU sensitivity and temperature-sensitive phenotypes of these rpb6 mutants were suppressed by overexpression of TFIIS, a transcription elongation factor. In agreement with the genetic studies, the mutant RNA polymerases containing the mutant Rpb6 subunits showed reduced affinity for TFIIS, as measured by a pull-down assay of TFIIS-RNA polymerase II complexes using a fusion form of TFIIS with glutathione S-transferase. Moreover, the direct interaction between TFIIS and RNA polymerase II was competed by the addition of Rpb6. Taken together, the results lead us to propose that Rpb6 plays a role in the interaction between RNA polymerase II and the transcription elongation factor TFIIS.

• Chen HT, Legault P, Glushka J, Omichinski JG, Scott RA
• Structure of a (Cys3His) zinc ribbon, a ubiquitous motif in archaeal and eucaryal transcription.
• Protein Sci. 2000; 9: 1743-52
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• Transcription factor IIB (TFIIB) is an essential component in the formation of the transcription initiation complex in eucaryal and archaeal transcription. TFIIB interacts with a promoter complex containing the TATA-binding protein (TBP) to facilitate interaction with RNA polymerase II (RNA pol II) and the associated transcription factor IIF (TFIIF). TFIIB contains a zinc-binding motif near the N-terminus that is directly involved in the interaction with RNA pol II/TFIIF and plays a crucial role in selecting the transcription initiation site. The solution structure of the N-terminal residues 2-59 of human TFIIB was determined by multidimensional NMR spectroscopy. The structure consists of a nearly tetrahedral Zn(Cys)3(His)1 site confined by type I and "rubredoxin" turns, three antiparallel beta-strands, and disordered loops. The structure is similar to the reported zinc-ribbon motifs in several transcription-related proteins from archaea and eucarya, including Pyrococcus furiosus transcription factor B (PfTFB), human and yeast transcription factor IIS (TFIIS), and Thermococcus celer RNA polymerase II subunit M (TcRPOM). The zinc-ribbon structure of TFIIB, in conjunction with the biochemical analyses, suggests that residues on the beta-sheet are involved in the interaction with RNA pol II/TFIIF, while the zinc-binding site may increase the stability of the beta-sheet.

• Donaldson IM, Friesen JD
• Zinc stoichiometry of yeast RNA polymerase II and characterization of mutations in the zinc-binding domain of the largest subunit.
• J Biol Chem. 2000; 275: 13780-8
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• Atomic absorption spectroscopy demonstrated that highly purified RNA polymerase II from the yeast Saccharomyces cerevisiae binds seven zinc ions. This number agrees with the number of potential zinc-binding sites among the 12 different subunits of the enzyme and with our observation that the ninth largest subunit alone is able to bind two zinc ions. The zinc-binding motif in the largest subunit of the enzyme was investigated using mutagenic analysis. Altering any one of the six conserved residues in the zinc-binding motif conferred either a lethal or conditional phenotype, and zinc blot analysis indicated that mutant forms of the domain had a 2-fold reduction in zinc affinity. Mutations in the zinc-binding domain reduced RNA polymerase II activity in cell-free extracts, even though protein blot analysis indicated that the mutant subunit was present in excess of wild-type levels. Purification of one mutant RNA polymerase revealed a subunit profile that was wild-type like with the exception of two subunits not required for core enzyme activity (Rpb4p and Rpb7p), which were missing. Core activity of the mutant enzyme was reduced 20-fold. We conclude that mutations in the zinc-binding domain can reduce core activity without altering the association of any of the subunits required for this activity.

• Loizos N, Darst SA
• Mapping interactions of Escherichia coli GreB with RNA polymerase and ternary elongation complexes.
• J Biol Chem. 1999; 274: 23378-86
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• Escherichia coli GreA and GreB modulate transcription elongation by interacting with the ternary elongation complex (containing RNA polymerase, DNA template, and RNA transcript) to induce hydrolytic cleavage of the transcript and release of the 3'-terminal fragment. Hydroxyl radical protein footprinting and alanine-scanning mutagenesis were used to investigate the interactions of GreB with RNA polymerase alone and in a ternary elongation complex. A major determinant for binding GreB to both RNA polymerase and the ternary elongation complex was identified. In addition, the hydroxyl radical footprinting indicated major conformational changes of GreB, in terms of reorientations of the N- and C-terminal domains with respect to each other, particularly upon interactions with the ternary elongation complex.

• Henry RW, Mittal V, Ma B, Kobayashi R, Hernandez N
• SNAP19 mediates the assembly of a functional core promoter complex (SNAPc) shared by RNA polymerases II and III.
• Genes Dev. 1998; 12: 2664-72
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• The basal transcription factor SNAPc binds to the PSE, a core element in the RNA polymerase II and III human snRNA promoters. SNAPc contains at least four subunits, but it has not been possible to assemble a fully defined recombinant SNAPc. Here we reconstitute SNAPc from five recombinant subunits, SNAP43, SNAP45, SNAP50, SNAP190, and a newly identified subunit, SNAP19. This recombinant complex binds specifically to the PSE and directs both RNA polymerase II and III snRNA gene transcription. Thus, the same core SNAPc nucleates the assembly of two classes of initiation complexes.

• Henry RW, Ford E, Mital R, Mittal V, Hernandez N
• Crossing the line between RNA polymerases: transcription of human snRNA genes by RNA polymerases II and III.
• Cold Spring Harb Symp Quant Biol. 1998; 63: 111-20

• Reinberg D et al.
• The RNA polymerase II general transcription factors: past, present, and future.
• Cold Spring Harb Symp Quant Biol. 1998; 63: 83-103

• Archambault J et al.
• FCP1, the RAP74-interacting subunit of a human protein phosphatase that dephosphorylates the carboxyl-terminal domain of RNA polymerase IIO.
• J Biol Chem. 1998; 273: 27593-601
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• TFIIF (RAP30/74) is a general initiation factor that also increases the rate of elongation by RNA polymerase II. A two-hybrid screen for RAP74-interacting proteins produced cDNAs encoding FCP1a, a novel, ubiquitously expressed human protein that interacts with the carboxyl-terminal evolutionarily conserved domain of RAP74. Related cDNAs encoding FCP1b lack a carboxyl-terminal RAP74-binding domain of FCP1a. FCP1 is an essential subunit of a RAP74-stimulated phosphatase that processively dephosphorylates the carboxyl-terminal domain of the largest RNA polymerase II subunit. FCP1 is also a stoichiometric component of a human RNA polymerase II holoenzyme complex.

• Olmsted VK et al.
• Yeast transcript elongation factor (TFIIS), structure and function. I: NMR structural analysis of the minimal transcriptionally active region.
• J Biol Chem. 1998; 273: 22589-94
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• TFIIS is a general transcription elongation factor that helps arrested RNA polymerase II elongation complexes resume transcription. We have previously shown that yeast TFIIS (yTFIIS) comprises three structural domains (I-III). The three-dimensional structures of domain II and part of domain III have been previously reported, but neither domain can autonomously stimulate transcription elongation. Here we report the NMR structural analysis of residues 131-309 of yTFIIS which retains full activity and contains all of domains II and III. We confirm that the structure of domain II in the context of fully active yTFIIS is the same as that determined previously for a shorter construct. We have determined the structure of the C-terminal zinc ribbon domain of active yTFIIS and shown that it is similar to that reported for a shorter construct of human TFIIS. The region linking domain II with the zinc ribbon of domain III appears to be conformationally flexible and does not adopt a single defined tertiary structure. NMR analysis of inactive mutants of yTFIIS support a role for the linker region in interactions with the transcription elongation complex.

• Legault P, Li J, Mogridge J, Kay LE, Greenblatt J
• NMR structure of the bacteriophage lambda N peptide/boxB RNA complex: recognition of a GNRA fold by an arginine-rich motif.
• Cell. 1998; 93: 289-99
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• The structure of the complex formed by the arginine-rich motif of the transcriptional antitermination protein N of phage lambda and boxB RNA was determined by heteronuclear magnetic resonance spectroscopy. A bent alpha helix in N recognizes primarily the shape and negatively charged surface of the boxB hairpin through multiple hydrophobic and ionic interactions. The GAAGA boxB loop forms a GNRA fold, previously described for tetraloops, which is essential for N binding. The fourth nucleotide of the loop extrudes from the GNRA fold to enable the E. coli elongation factor NusA to recognize the N protein/RNA complex. This structure reveals a new mode of RNA-protein recognition and shows how a small RNA element can facilitate a protein-protein interaction and thereby nucleate formation of a large ribonucleoprotein complex.

• Pardee TS, Bangur CS, Ponticelli AS
• The N-terminal region of yeast TFIIB contains two adjacent functional domains involved in stable RNA polymerase II binding and transcription start site selection.
• J Biol Chem. 1998; 273: 17859-64
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• The general transcription factor IIB (TFIIB) is required for accurate and efficient transcription of protein-coding genes by RNA polymerase II (RNAPII). To define functional domains in the highly conserved N-terminal region of TFIIB, we have analyzed 14 site-directed substitution mutants of yeast TFIIB for their ability to support cell viability, transcription in vitro, accurate start site selection in vitro and in vivo, and to form stable complexes with purified RNAPII in vitro. Mutations impairing the formation of stable TFIIB.RNAPII complexes mapped to the zinc ribbon fold, whereas mutations conferring downstream shifts in transcription start site selection were identified at multiple positions within a highly conserved homology block adjacent and C-terminal to the zinc ribbon. These results demonstrate that the N-terminal region of yeast TFIIB contains two separable and adjacent functional domains involved in stable RNAPII binding and transcription start site selection, suggesting that downstream shifts in transcription start site selection do not result from impairment of stable TFIIB.RNAPII binding. We discuss models for yeast start site selection in which TFIIB may affect the ability of preinitiation complexes to interact with downstream DNA or to affect start site recognition by a scanning polymerase.

• Morin PE, Awrey DE, Edwards AM, Arrowsmith CH
• Elongation factor TFIIS contains three structural domains: solution structure of domain II.
• Proc Natl Acad Sci U S A. 1996; 93: 10604-8
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• Transcription elongation by RNA polymerase II is regulated by the general elongation factor TFIIS. This factor stimulates RNA polymerase II to transcribe through regions of DNA that promote the formation of stalled ternary complexes. Limited proteolytic digestion showed that yeast TFIIS is composed of three structural domains, termed I, II, and III. The two C-terminal domains (II and III) are required for transcription activity. The structure of domain III has been solved previously by using NMR spectroscopy. Here, we report the NMR-derived structure of domain II: a three-helix bundle built around a hydrophobic core composed largely of three tyrosines protruding from one face of the C-terminal helix. The arrangement of known inactivating mutations of TFIIS suggests that two surfaces of domain II are critical for transcription activity.

• Wu J, Awrey DE, Edwards AM, Archambault J, Friesen JD
• In vitro characterization of mutant yeast RNA polymerase II with reduced binding for elongation factor TFIIS.
• Proc Natl Acad Sci U S A. 1996; 93: 11552-7
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• We have reported previously the isolation and genetic characterization of mutations in the gene encoding the largest subunit of yeast RNA polymerase II (RNAPII), which lead to 6-azauracil (6AU)-sensitive growth. It was suggested that these mutations affect the functional interaction between RNAPII and transcription-elongation factor TFIIS because the 6AU-sensitive phenotype of the mutant strains was similar to that of a strain defective in the production of TFIIS and can be suppressed by increasing the dosage of the yeast TFIIS-encoding gene, PPR2, RNAPIIs were purified and characterized from two independent 6AU-sensitive yeast mutants and from wild-type (wt) cells. In vitro, in the absence of TFIIS, the purified wt polymerase and the two mutant polymerases showed similar specific activity in polymerization, readthrough at intrinsic transcriptional arrest sites and nascent RNA cleavage. In contrast to the wt polymerase, both mutant polymerases were not stimulated by the addition of a 3-fold molar excess of TFIIS in assays of promoter-independent transcription, readthrough or cleavage. However, stimulation of the ability of the mutant RNAPIIs to cleave nascent RNA and to read through intrinsic arrest sites was observed at TFIIS:RNAPII molar ratios greater than 600:1. Consistent with these findings, the binding affinity of the mutant polymerases for TFIIS was found to be reduced by more than 50-fold compared with that of the wt enzyme. These studies demonstrate that TFIIS has an important role in the regulation of transcription by yeast RNAPII and identify a possible binding site for TFIIS on RNAPII.

• Cipres-Palacin G, Kane CM
• Alanine-scanning mutagenesis of human transcript elongation factor TFIIS.
• Biochemistry. 1995; 34: 15375-80
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• TFIIS is a transcription elongation factor that binds to RNA polymerase II and allows it to transcribe through a variety of transcriptional blockages by inducing cleavage near the 3' end of the nascent transcript. Although this cleavage reaction plays a key role in the process of reactivation of transcription by TFIIS, the exact mechanism by which TFIIS promotes readthrough by RNA polymerase II is not completely understood. We therefore undertook a systematic mutagenesis of the C-terminal half of TFIIS (delta TFIIS) to evaluate the contribution of charged residues in this region to induce transcript cleavage and promote readthrough in vitro. Twenty-two delta TFIIS alanine-scanning mutants were constructed by substitution of alanine for each amino acid in clusters of charged residues in the C-terminal half of HeLa TFIIS. The ability to induce transcript cleavage and readthrough of these mutants was tested in vitro using RNA polymerase II ternary elongation complexes arrested at a block to elongation. This alanine-scanning mutagenesis analysis allowed the identification of regions or residues important for the activity of TFIIS. Many of the mutants were reduced alike in both cleavage and readthrough activities. However, in several cases there was no simple correlation between these activity reductions.

• Jeon C, Yoon H, Agarwal K
• The transcription factor TFIIS zinc ribbon dipeptide Asp-Glu is critical for stimulation of elongation and RNA cleavage by RNA polymerase II.
• Proc Natl Acad Sci U S A. 1994; 91: 9106-10
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• The eukaryotic transcription factor TFIIS enhances elongation and nascent transcript cleavage activities of RNA polymerase II in a stalled elongation complex. By site-directed mutagenesis, we have demonstrated that invariant residues Asp-261 and Glu-262 of the nucleic acid-binding TFIIS Zn ribbon are critical for stimulation of both elongation and RNA cleavage activities of RNA polymerase II. Substitution of either of these residues inactivates both TFIIS functions, suggesting a related role in both activities. These acidic residues may participate in phosphoryl transfer reactions by a two-metal-ion mechanism in a manner analogous to Klenow fragment. The RNA polymerase II itself may contain a Zn ribbon, in as much as the polymerase's 15-kDa subunit contains a sequence that aligns well with the TFIIS Zn ribbon sequence, including a similarly placed pair of acidic residues.

• Park H, Baek K, Jeon C, Agarwal K, Yoo O
• Characterization of the gene encoding the human transcriptional elongation factor TFIIS.
• Gene. 1994; 139: 263-7
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• The transcriptional elongation factor TFIIS causes stimulation of RNA polymerase II elongation and readthrough of some of the elongation blocks. We present cloning and sequence characterization of the human TFIIS gene and a pseudogene. The intron-less organization of both of these genes indicates that previously identified cDNAs which suggested the presence of an intron were the products of cloning artifacts. The gene is organized in an uninterrupted ORF which codes for 301 amino acids, whereas the pseudogene lacks an ORF able to code for a full-length protein. The potential promoter for the gene has two putative GC-box-type consensus sequences, two CCAAT-box consensus sequences, and is bounded by a human Alu sequence. Two potential transcriptional termination signal sequences downstream from the consensus polyadenylation signal are proposed.

• Cipres-Palacin G, Kane CM
• Cleavage of the nascent transcript induced by TFIIS is insufficient to promote read-through of intrinsic blocks to elongation by RNA polymerase II.
• Proc Natl Acad Sci U S A. 1994; 91: 8087-91
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• RNA polymerases encounter a variety of types of blocks to elongation during transcription in eukaryotic cells. At least one protein, TFIIS, can promote read-through of many types of blocks to elongation by RNA polymerase II, and this protein stimulates cleavage of the nascent transcript in stalled elongation complexes as a prelude to read-through. The C-terminal half of the TFIIS protein is sufficient for stimulating the cleavage and read-through reactions in vitro. To study how TFIIS changes the response of RNA polymerase II elongation complexes to such blocks, targeted amino acids in the C terminus of HeLa TFIIS were mutated to alanines. Two mutant TFIIS proteins as well as the unmutated C-terminal half of the TFIIS protein were purified following overexpression in Escherichia coli. Each protein was examined for read-through activity and ability to stimulate transcript cleavage in ternary elongation complexes. Mutant TFIIS5 (E174A, E175A) was reduced in read-through and cleavage activities relative to the unmutated, truncated TFIIS (delta TFIIS). Mutant TFIIS7 (K187A, K189A) was able to stimulate cleavage nearly at the rate and to the extent of the TFIIS5 mutant. In contrast to what was observed with TFIIS5, no detectable read-through was observed in the presence of the TFIIS7 mutant during the course of the reaction. Thus, there is no simple, direct correlation between the ability of TFIIS to promote cleavage and its ability to promote read-through by RNA polymerase II. These results suggest that although TFIIS is necessary to mediate the cleavage reaction that precedes the read-through event, the cleavage event itself is not sufficient to allow read-through by RNA polymerase II.

• Qian X, Gozani SN, Yoon H, Jeon CJ, Agarwal K, Weiss MA
• Novel zinc finger motif in the basal transcriptional machinery: three-dimensional NMR studies of the nucleic acid binding domain of transcriptional elongation factor TFIIS.
• Biochemistry. 1993; 32: 9944-59
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• Transcriptional elongation provides a key control point in the regulation of eukaryotic gene expression. Here we describe homonuclear and 15N-heteronuclear 3D NMR studies of the nucleic acid binding domain of human transcriptional elongation factor TFIIS. This domain contains a Cys4 Zn(2+)-binding site with no homology to previously characterized Cys4, Cys6, or Cys2-His2 Zn fingers. Complete 1H and 15N NMR resonance assignment of a 50-residue TFIIS peptide-Zn2+ complex is obtained. Its solution structure, as determined by distance geometry/simulated annealing (DG/SA) calculations, exhibits a novel three-stranded antiparallel beta-sheet (designated the Zn ribbon). Analogous sequence motifs occur in a wide class of proteins involved in RNA or DNA transactions, including human basal transcriptional initiation factor TFIIE. A three-dimensional model of the TFIIE Cys4 domain is obtained by DG-based homology modeling. The role of the TFIIS Zn ribbon in the control of eukaryotic transcriptional elongation is discussed.