Practice question

Co-transcriptional histone modifications demarcate functional regions of transcribed units. During elongation, Ser2-phosphorylated C-terminal domain of RNA polymerase II recruits Set2 methyltransferase via interaction with PAF complex and Spt6 chaperone, leading to trimethylation of H3K36 over gene bodies. H3K36me3 suppresses cryptic initiation by recruiting Rpd3S deacetylase and Isw1b remodeler, preserving nucleosome integrity behind polymerase. It also influences alternative splicing by binding MRG15 and splicing regulators. Unlike promoter-associated H3K4me3, H3K36me3 peaks toward 3' ends of active genes, marking productive elongation and preventing spurious transcription.