Mechanisms of Histone Chaperones and Chromatin Remodelers in Transcription Elongation

• Published in: The FASEB journal 2010-04, Vol.24 (S1), p.lb65-lb65
• Main Authors: Kuryan, Benjamin George, Carey, Michael
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.24.1_supplement.lb65

It is established that nucleosomes pose a barrier to elongating RNA Polymerase II (Pol II), but the mechanisms by which this is overcome are still largely unknown. In vivo, the nucleosomal barrier is likely abrogated through the coordinated activities of various enzymes including ATP‐dependent chromatin remodelers (ATPases) and histone chaperones. We have developed a biochemical system whereby transcription through a nucleosome is dependent on both the activity of the ATPase complex “Remodels Structure of Chromatin” (RSC) and the histone chaperone “Nucleosome Assembly Protein 1” (Nap1). RSC alone stimulates elongation through the nucleosome, but depends on an acceptor DNA molecule to receive the octamer evicted from the transcribed template. We find that Nap1 stimulates RSC‐dependent transcription in the absence of an acceptor DNA molecule. However, Nap1 inhibits RSC‐mediated octamer transfer, but not remodeling. In reactions with RSC and Nap1, an H2A‐H2B dimer is lost. These data support a model where RSC evicts the octamer from the template to facilitate Pol II passage and Nap1 reassembles a hexasome in cis. Formation of this hexasome is consistent with previous studies of transcription through nucleosomes where transcription was dependent on high salt conditions to loosen the histone‐DNA contacts. We have now shown this occurs enzymatically through Nap1‐mediated RSC remodeling.