Defining a direct mechanism of ESCO1 in chromatin organization

Project Summary/Abstract: DNA in a cell nucleus is organized on multiple levels. The Cohesin complex organizes DNA into large loops and domains. This level of organization is critical for normal chromosome structure and function. ESCO1 is an acetyltransferase enzyme that regulates chromosome organization and gene expression by modifying Cohesin. Acetylation of the SMC3 subunit of Cohesin by ESCO1 stabilizes Cohesin on DNA, promoting long residence time. ESCO1 and Cohesin colocalize at the base of chromatin loops, but ESCO1 is driven to chromatin through its highly basic and disordered N-terminal tail, independently of Cohesin. Interestingly, ESCO1 is suggested to influence genome organization independent of Cohesin acetylation. The mechanism(s) driving these Cohesin-independent functions is unclear. We have found that tethering multiple copies of ESCO1 to a specific location in the nucleus results in gross local rearrangement of chromatin. Strikingly, this Local Chromatin Rearrangement (LCR) occurs independently of ESCO1’s acetyltransferase activity and does not occur through Cohesin. To determine what about ESCO1 was driving this LCR, we performed a small screen of DNA binding proteins and showed that linker histone drove rearrangement in a manner similar to ESCO1. This has led us to propose that ESCO1 has intrinsic linker histone-like activity. we will challenge this model directly by defining the effect ESCO1 has on chromatin structure and function. We hypothesize that the N-terminal tail of ESCO1 binds DNA to condense and rearrange chromatin, perhaps explaining ESCO1’s Cohesin-independent functions. In these experiments, we will define the effect of the ESCO1 tail on chromatin organization and function in cells (Aim 1) and measure the impact of the ESCO1-chromatin interaction on chromatin structure in vitro (Aim 2). This work will fundamentally improve our understanding of DNA organization in vertebrate systems.