Our Science – Wu Website
Carl Wu, Ph.D.
We have an enduring interest in the role of chromatin architecture in gene expression and chromosome functions, with the goal of discovering fundamental principles of chromatin biology. The knowledge we gain is critical to understanding the complex rules that govern normal cell growth and differentiation, and the collapse of cellular regulation in diseases like cancer. Our approach is to develop unbiased biochemical assays for key chromosome functions and to purify the responsible molecules from cell extracts. We then confirm physiological significance by genetics, and elucidate mechanisms of action with native and reconstituted components, using every available tool of modern biology.
NURF is a prototypical chromatin remodeling enzyme that catalyzes nucleosome sliding for gene activation or repression. Knockouts of the largest NURF subunit, NURF301/BPTF, uncovered its requirement for the regulation of hundreds of genes, and for embryonic and post-embryonic development in the fly and mouse. At a molecular level, NURF is recruited to specific gene targets by a limited number of sequence-specific transcription factors, and by bromo- and PHD-domain interactions with acetylated and methylated histones. Findings support a general model in which sequence-specific factor binding, histone modification and targeted nucleosome repositioning generate nucleosome-free or occluded DNA, thereby controlling access by the transcriptional machinery. Paul Badenhorst (U. of Birmingham, UK), and Joe Landry (Virginia Commonwealth U.) now continue this work.
The histone variant H2A.Z is also implicated in the control of transcription, and is strikingly incorporated in nucleosomes surrounding eukaryotic promoters and regulatory elements genome-wide. Amongst the large family of chromatin remodeling enzymes, the conserved, multi-subunit SWR1 complex is uniquely dedicated to the replacement of nucleosomal histone H2A with H2A.Z. Upon recruitment to promoters, the SWR1 complex catalyzes eviction of H2A-H2B dimers from conventional nucleosomes, and the deposition of H2A.Z-H2B. We are currently exploring the molecular mechanism by which SWR1 mediates this reaction, and the effects of the resulting nucleosome products on transcription.
Another histone variant, CenH3, is universally incorporated in centromeric chromatin, and is fundamental to kinetochore assembly and chromosome segregation in mitosis and meiosis. The molecular architecture of CenH3 nucleosomes has been controversial. Biochemical analysis of CenH3 interacting proteins in budding yeast revealed Scm3, a nonhistone protein that is required for CenH3 deposition and kinetochore function. Scm3 has two domains: one binds specifically to CenH3-H4, acting as a histone chaperone; the other binds preferentially to AT-rich centromere DNA, blocking the association of H2A-H2B dimers. In consequence, a highly atypical nucleosome that contains only one out of four conventional histones appears to form on centromeric chromatin in budding yeast. We are investigating the molecular architecture of this atypical nucleosome and the mechanism by which it directs kinetochore assembly and function.
Xiao H, Mizuguchi G, Wisniewski J, Huang Y, Wei D, Wu C. Nonhistone Scm3 Binds to AT-Rich DNA to Organize Atypical Centromeric Nucleosome of Budding Yeast. Mol Cell 43:369-80 (2011).
Luk E, Ranjan A, Fitzgerald PC, Mizuguchi G, Huang Y, Wei D, Wu C. Stepwise Histone Replacement by SWR1 Requires Dual Activation with Histone H2A.Z and Canonical Nucleosome. Cell 143:725-36 (2010).
Mizuguchi G, Xiao H, Wisniewski J, Smith M.M and Wu C. Nonhistone Scm3 and histones CenH3-H4 assemble the core of centromere specific nucleosomes. Cell 129: 1153-1164 (2007).
Mizuguchi G, Shen X, Landry J, Wu W.H, Sen S, and Wu C. ATP-driven exchange of histone H2AZ variant catalyzed by SWR1 chromatin remodeling complex. Science 303: 343-348 (2004).
This page was last updated on 8/8/2012.