Poster abstracts
Poster number 53 submitted by A. Elizabeth Hildreth
Identifying the regulatory role of the DNA entry-exit site of the nucleosome in transcription termination
A. Elizabeth Hildreth (Department of Biological Sciences, University of Pittsburgh), Karen M. Arndt, PhD (Department of Biological Sciences, University of Pittsburgh)
Abstract:
Eukaryotic chromatin is a restrictive barrier to RNA polymerase II, which transcribes protein coding and some noncoding RNAs. Chromatin consists of repeating nucleosomes, approximately 147 basepairs of DNA surrounding an octamer of histone proteins. Transcription is controlled by factors that modify nucleosomes, allowing Pol II to contact otherwise occluded DNA. The mechanisms by which chromatin is modified are well understood in regard to transcription initiation and elongation. Despite a few studies showing a requirement for select histone modifications and chromatin remodelers, little else is known about the role of chromatin at the final termination step. The goal of our work is to elucidate this role using Saccharomyces cerevisiae. We used a plasmid library encoding mutant histones and a termination reporter to identify 12 residues in histones H3, H4, and H2A required for proper termination. Interestingly, many of these residues reside in or near the nucleosome DNA entry-exit site. This surface coordinates the first 30 basepairs of DNA, thus regulating stability and accessibility of the nucleosome. Analysis thus far reveals improper nucleosome occupancy at candidate loci and defective placement of a transcription-coupled histone modification. Recent results suggest that increased elongation rate may also contribute to the observed termination defect in some mutants. These data implicate the DNA entry-exit site as an important player in the regulation of transcription.
Keywords: transcription, termination, chromatin