title: Histone release during transcription: displacement of the two H2A-H2B dimers in the nucleosome is dependent on different levels of transcription-induced positive stress.
abstract: Both indirect (transcription-induced stress) and direct effects of polymerase elongation on histone-DNA interactions were studied on closed circular DNA that was either moderately or positively coiled. The templates were reconstituted with (3)H-labeled H2A, H2B, H3, and H4 to form nucleosomes, and transcription was done with T7 RNA polymerase in the presence of a negatively coiled competitor DNA (reconstituted with unlabeled H3 and H4). The first of the two labeled H2A-H2B dimers readily displaced from the highly positively coiled template to the competitor even in the absence of transcription, while the indirect effect of transcription-induced stress was required for the moderately coiled template. The second labeled H2A-H2B dimer required transcription-induced stress for both moderately and highly positively coiled DNA. The displacement of the labeled H3-H4 tetramer also occurred, provided it was associated with an H2A-H2B dimer and a moderately positively coiled DNA. This displacement occurred independent of transcription-induced stress and is likely due to the direct effect of polymerase disruption of histone-DNA interactions. The inclusion of the histone chaperone, NAP1, greatly enhanced the release of both of the two H2A-H2B dimers. These observations are consistent with in vivo observations which indicate that during transcription H2A and H2B are significantly more mobile than H3 and H4 and indicate that transcription-induced positive stress is a likely cause for this selective movement.
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226, USA.
authors.forename: Vladislav
authors.initials: V
authors.lastname: Levchenko
authors.forename: Beverly
authors.initials: B
authors.lastname: Jackson
authors.forename: Vaughn
authors.initials: V
authors.lastname: Jackson
mesh_terms: D000818:Animals; D002645:Chickens; D019281:Dimerization; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D009707:Nucleosomes / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D006657:Histones; D009707:Nucleosomes