Short conserved domain in transcriptional regulators.
SMART accession number:SM00719
Description: Plus3 domains occur in the Saccharomyces cerevisiae Rtf1p protein, which interacts with Spt6p, and in parsley CIP, which interacts with the bZIP protein CPRF1.
Interpro abstract (IPR004343):

The yeast Paf1 complex consists of Pfa1, Rtf1, Cdc73, Ctr9, and Leo1. The complex regulates histone H2B ubiquitination, histone H3 methylation, RNA polymerase II carboxy-terminal domain (CTD) Ser2 phosphorylation, and RNA 3' end processing. The conservation of Paf1 complex function in higher eukaryotes has been confirmed in human cells, Drosophila and Arabidopsis. The Plus3 domain spans the most conserved regions of the Rtf1 protein and is surrounded by regions of low complexity and coiled-coil propensity [ (PUBMED:11014804) ]. It contains only a limited number of highly conserved amino acids, among which are three positively charged residues that gave the Plus3 domain its name. The capacity to bind single-stranded DNA is at least one function of the Plus3 domain [ (PUBMED:18184592) ].

The plus-3 domain is about 90 residues in length and is often found associated with the GYF domain ( IPR003169 ). The Plus3 domain structure consists of six alpha helices intervened by a sequence of six beta strands in a mixed alpha/beta topology. Beta strands 1, 2, 5, and 6 compose a four-stranded antiparallel beta sheet with a beta-hairpin insertion formed by strands 3 and 4. The N-terminal helices alpha1-alpha3 and C-terminal helix alpha6 pack together to form an alpha subdomain, while the beta strands and the small 3(10) helix alpha 4 form a beta subdomain. The two subdomains pack together to form a compact, globular protein [ (PUBMED:18184592) ].

GO function:DNA binding (GO:0003677)
Family alignment:
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There are 1155 Plus3 domains in 1149 proteins in SMART's nrdb database.

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