Paf1 complex subunit Rtf1 stimulates H2B ubiquitylation by interacting with the highly conserved N-terminal helix of Rad6.

Histone modifications coupled to transcription elongation play important roles in regulating the accuracy and efficiency of gene expression. The monoubiquitylation of a conserved lysine in H2B (K123 in ; K120 in humans) occurs cotranscriptionally and is required for initiating a histone modification cascade on active genes. H2BK123 ubiquitylation (H2BK123ub) requires the RNA polymerase II (RNAPII)-associated Paf1 transcription elongation complex (Paf1C).

The nucleosome acidic patch directly interacts with subunits of the Paf1 and FACT complexes and controls chromatin architecture in vivo.

The nucleosome core regulates DNA-templated processes through the highly conserved nucleosome acidic patch. While structural and biochemical studies have shown that the acidic patch controls chromatin factor binding and activity, few studies have elucidated its functions in vivo. We employed site-specific crosslinking to identify proteins that directly bind the acidic patch in Saccharomyces cerevisiae and demonstrated crosslinking of histone H2A to Paf1 complex subunit Rtf1 and FACT subunit Spt16.