A role for histones H2A/H2B in chromatin folding and transcriptional repression.
Histone octamers or histone H3/H4 tetramers were reconstituted onto either closed circular plasmids containing a single Xenopus 5S rRNA gene or a reiterated array of Lytechinus 5S rRNA genes. All "reconstitutes" were found to undergo both Na(+)-dependent and Mg(2+)-dependent compaction. However, in each case, the compaction of nucleosomal templates containing H2A/H2B was much more extensive than compaction of templates containing only H3/H4 tetramers. Inclusion of 5 mM MgCl2 in the transcription buffer increased the level of compaction of nucleosomal templates and led to a marked inhibition of both transcription initiation and elongation by RNA polymerase III. The inhibitory effect of Mg2+ was reduced significantly when DNA templates contained only H3/H4 tetramers, consistent with their lesser extent of Mg(2+)-dependent compaction. Thus, the removal of histones H2A/H2B from nucleosomal arrays enhances gene activity, in part because of decreased levels of chromatin folding.
Hansen
J C
JC
Department of Biochemistry, University of Texas Health Science Center at San Antonio 78284-7760.
Wolffe
A P
AP
D000818:Animals; D002021:Buffers; D002645:Chickens; D002843:Chromatin / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D006657:Histones / Q000502:physiology*; D008274:Magnesium / Q000378:metabolism; D008836:Micrococcal Nuclease / Q000378:metabolism; D009707:Nucleosomes / Q000378:metabolism; D017510:Protein Folding; D012320:RNA Polymerase III / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D014158:Transcription, Genetic; D014982:Xenopus laevis
D002021:Buffers; D002843:Chromatin; D006657:Histones; D009707:Nucleosomes; D012097:Repressor Proteins; D012320:RNA Polymerase III; D008836:Micrococcal Nuclease; D008274:Magnesium