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EMBO J. 1997 Apr 15;16(8):2086-95.

Effects of Sin- versions of histone H4 on yeast chromatin structure and function.

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Program in Molecular Medicine and Department of Biochemistry and Molecular Biology, University of Massachusetts Medical Center, Worcester 01605, USA.


Previous studies have identified single amino acid changes within either histone H3 or H4 (Sin- versions) that allow transcription in the absence of the yeast SWI-SNF complex. The histone H4 mutants are competent for nucleosome assembly in vivo, and the residues that are altered appear to define a discrete domain on the surface of the histone octamer. We have analyzed the effects of the Sin- versions of histone H4 on transcription and chromatin structure in vivo. These histone H4 mutants cause an increased accessibility of nucleosomal DNA to Dam methyltransferase and to micrococcal nuclease. Sin- derivatives of histone H4 also grossly impair the ability of nucleosomes to constrain supercoils in vivo. Nucleosome-mediated repression of the PHO5 gene is severely impaired by these histone H4 mutants; PHO5 expression is derepressed to 31% of the wild-type induced level. In contrast to the induction caused by nucleosome depletion, full PHO5 derepression by Sin- versions of histone H4 requires upstream regulatory elements. In addition, Sin- derivatives of histone H4 do not activate expression from CYC1 or GAL1 promoters that lack UAS elements. We propose that these Sin- mutations alter histone-DNA contact residues that play key roles in restricting the accessibility of nucleosomal DNA to transcription factors.

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