Illustrations reflects the relevant components, but not precise physical association or order of events. A At the early stages of transcription, the PAF complex and CTD S5-P form of RNAPII are required for monoubiquitylation of histone H2B on lysine 123 by Rad6-Bre1. H2B ubiquitylation drives promoter association of the COMPASS/Set1 methyltransferase, which methylates histone H3 on lysine 