DNA Bridging and Looping by Hmo1 Provides a Mechanism for Stabilizing Nucleosome-Free Chromatin

When: Wednesday, January 29, 2014 at 12:00 pm
Where: DA 114
Speaker: Divakaran Murugesapillai
Organization: Northeastern University
Sponsor: Introduction to Physics Research

The regulation of complex chromatin structure in eukaryotic cells involves abundant architectural factors such as High Mobility Group B (HMGB) proteins. The yeast Hmo1 protein contains one canonical HMGB domain and a second HMG-like domain implicated in dimerization. in vivo, Hmo1 binds to the promoter and coding regions of most ribosomal RNA genes, facilitating transcription and stabilizing chromatin in the absence of histones. To understand how Hmo1 performs these functions, we combine single molecule stretching and atomic force microscopy (AFM). By stretching Hmo1-bound DNA, we quantify Hmo1-DNA interactions. Hmo1 proteins initially compact DNA, then form DNA bridges and stabilize DNA loops. By pulling on these loops, we characterize their size and stability. AFM experiments confirm DNA bridging and looping by Hmo1. Taken together, our results support a model in which Hmo1 maintains the stability of nucleosome-free chromatin regions by forming complex structures induced by dimerization of DNA-bound proteins.