Chromatin remodelers Isw1 and Chd1 maintain chromatin structure during transcription by preventing histone exchange.
Set2-mediated methylation of histone H3 Lys36 (H3K36) is a mark associated with the coding sequences of actively transcribed genes, but it has a negative role during transcription elongation. It prevents trans-histone exchange over coding regions and signals for histone deacetylation in the wake of RNA polymerase II (RNAPII) passage. We have found that in Saccharomyces cerevisiae the Isw1b chromatin-remodeling complex is specifically recruited to open reading frames (ORFs) by H3K36 methylation through the PWWP domain of its Ioc4 subunit in vivo and in vitro. Isw1b acts in conjunction with Chd1 to regulate chromatin structure by preventing trans-histone exchange from taking place over coding regions. In this way, Isw1b and Chd1 are important in maintaining chromatin integrity during transcription elongation by RNAPII.