%0 Journal Article
%T SWI/SNF-mediated chromatin remodeling induces Z-DNA formation on a nucleosome
%A Niveen Mulholland
%A Yan Xu
%A Hiroshi Sugiyama
%A Keji Zhao
%J Cell & Bioscience
%D 2012
%I BioMed Central
%R 10.1186/2045-3701-2-3
%X We show that remodeling of a mononucleosome by the human SWI/SNF complex results in Z-DNA formation when the DNA within the mononucleosome contains Z-DNA favoring sequence. Nuclease accessibility patterns of nucleosome core particle consisting of Z-DNA are quite different from counterpart nucleosomes containing classic B-DNA. Z-nucleosomes represent a novel mononucleosome structure.We present evidence that Z-DNA can form on nucleosomes though previous observations indicate the occlusion of nucleosome formation from Z-DNA.Sequences with alternating purine and pyrimidine repeats have the highest Z-DNA forming potential [1] and are enriched in promoter regions [2]. The generation of negative supercoils behind an actively transcribing RNA polymerase [3] or by SWI/SNF-mediated nucleosome remodeling [4] can result in Z-DNA formation at promoters with TG or GC repeats. For example, TG repeats in the CSF1 gene promoter adopt a Z-DNA conformation when transcription is activated by BRG1, the ATP-dependent subunit of SWI/SNF [5]. BRG1 activity induced Z-DNA formation even in the absence of transcription indicating the torsional strain required for Z-DNA formation is generated by nucleosome remodeling rather than an actively transcribing polymerase [6]. Nucleosome mapping of the CSF1 promoter revealed that these Z-DNA forming repeats are incorporated in a nucleosome prior to BRG1 activation.In vitro studies examining the interactions between Z-DNA and histones suggest that Z-DNA associates with histones but does not incorporate into a nucleosome [7]. The activity we have observed on the CSF1 promoter in vivo, prompted us to reexamine this issue. As the most basic unit of chromatin, the mononucleosome has proven to be an invaluable tool for probing the mechanisms used in transcriptional activation as well as for many other cellular functions. Since detection of Z-DNA structure in vivo at a genomic position associated with a nucleosome may not necessarily indicate formation of Z-
%U http://www.cellandbioscience.com/content/2/1/3