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. Structural domains comprising this superfamily share the structure of the conserved and functionally important Plus3 domain of human Rtf1. This predominantly beta-stranded subdomain displays structural similarity to Dicer/Argonaute PAZ domains and Tudor domains. The plus-3 domain spans the most conserved regions of the Rtf1 protein and is surrounded by regions of low complexity and coiled-coil propensity PMID:11014804. It contains a limited number of highly conserved amino acids, three of which are positively charged residues, reason behind this domains name. Plus3 Is structurally and functionally related to other nucleic acid binding domains and its capacity to bind single-stranded DNA is at least one of the functions of the Plus3 domain PMID:18184592.