Effects of Sin- versions of histone H4 on yeast chromatin structure and function.
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.
Wechser
M A
MA
Program in Molecular Medicine and Department of Biochemistry and Molecular Biology, University of Massachusetts Medical Center, Worcester 01605, USA.
Kladde
M P
MP
Alfieri
J A
JA
Peterson
C L
CL
D002843:Chromatin / Q000737:chemistry*; D015825:Chromosomes, Fungal / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics; D004278:DNA, Superhelical; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D005800:Genes, Fungal / Q000235:genetics; D006657:Histones / Q000737:chemistry* / Q000235:genetics; D026901:Membrane Transport Proteins / Q000235:genetics; D008836:Micrococcal Nuclease; D009154:Mutation; D028061:Phosphate Transport Proteins; D011993:Recombinant Fusion Proteins; D012045:Regulatory Sequences, Nucleic Acid; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D014158:Transcription, Genetic / Q000502:physiology*; D015003:Yeasts / Q000737:chemistry / Q000235:genetics
D002843:Chromatin; D004271:DNA, Fungal; D004278:DNA, Superhelical; D006657:Histones; D026901:Membrane Transport Proteins; D028061:Phosphate Transport Proteins; D011993:Recombinant Fusion Proteins; C055831:phosphate permease; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D008836:Micrococcal Nuclease