The B-WICH chromatin-remodelling complex initiates the regulation of RNA polymerase III by c-Myc

Abstract

Transcription by RNA polymerase III in eukaryotic cells is closely associated with cell growth and proliferation, and regulated by several proliferative signals. In addition, the chromatin-remodelling complex B-WICH, comprised of William syndrome transcription factor, the ATPase SNF2h and nuclear myosin, binds to the 5S rRNA and 7SL genes and activates transcription, but the mechanism behind is poorly understood. Here, we have used high‑resolution MN walking to show that the role of B-WICH in RNA polymerase III transcription is to induce local alterations of the chromatin structure in the vicinity of the 5S rRNA and 7SL RNA genes. In the 5S rDNA, the remodelled region harbours an E-box, to which c-Myc, together with Max, binds in a B-WICH dependent way.  Both B-WICH and c-Myc are required for the subsequent histone acetylation of histone H3. Our results present two ways for c-Myc to alter 5S rRNA transcription; to bind to the RNA polymerase III machinery at the promoter and to an E-box in the intergenic spacer. We propose a model in which the B-WICH complex is required to maintain an open chromatin structure at these RNA polymerase III genes, which is a prerequisite for other regulatory factors to bind at the gene.</p