Chromatin structure and Expression of a gene transcribed by RNA polymerase III are independent of H2A.Z deposition

Centre for Cellular and Molecular Biology, Uppal Road, Tarnaka, Hyderabad-500007, INDIA

^* To whom correspondence should be addressed. Email: purnima{at}ccmb.res.in.

	Abstract

The genes transcribed by RNA polymerase III (pol III) generally have intragenic promoter elements. One of them, the yeast U6 snRNA (SNR6) gene is activated in vitro by a positioned nucleosome between its intragenic box A and extragenic, downstream box B separated by 200 bp. We demonstrate here that the in vivo chromatin structure of gene is characterized by the presence of an array of positioned nucleosomes, with only one of them in the 5' end of the gene having a regulatory role. A positioned nucleosome present between the boxes A and B in vivo does not move when the gene is repressed due to nutritional deprivation. In contrast, the upstream nucleosome which covers the TATA box under repressed condition; is shifted 50 bp upstream by an ATP-dependent chromatin remodeler RSC upon activation. It is marked with histone variant H2A.Z and H4K16 acetylation in active state. In the absence of H2A.Z, the chromatin structure of the gene does not change, suggesting H2A.Z is not required for establishing the active chromatin structure. These results show that the chromatin structure directly participates in regulation of a pol III-transcribed gene under different states of its activity in vivo.