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Renaturase and ribonuclease H: a novel mechanism that influences transcript displacement by RNA polymerase II in vitro 总被引:9,自引:0,他引:9
C M Kane 《Biochemistry》1988,27(9):3187-3196
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To study the structural and functional changes accompanying the integration of histone H5 into the nucleosome structure, linear DNA species have been employed with a terminal promoter for bacteriophage T7 RNA polymerase followed by tandem repeats of a 207-bp nucleosome positioning sequence. The oligonucleosomes assembled from 12-repeat DNA and saturating amounts of core histone octamer plus histone H5 are compacted, in the presence of 1 mM free magnesium ions, to the level of the 30-nm fiber. Under these ionic conditions the efficiency in RNA synthesis and the size distribution of RNA chains obtained with this template are the same as those corresponding to the template without H5, indicating that the 30-nm fiber stabilized by H5 does not impair RNA elongation. Therefore, under our experimental conditions, incorporation of one molecule of histone H5 per nucleosome does not affect elongation of RNA even when a folded structure is produced. However, elongation is inhibited by binding of an excess of H5. 相似文献
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It has been reported (Iborra et al. (1979) J. Biol. Chem. 254, 10920-10924) that the third and the fifth largest subunit of yeast RNA polymerase I exhibit ribonuclease H activity. The authors suggested that the third largest subunit is identical with the chromatin-associated ribonuclease H49, the putative yeast equivalent of bovine ribonuclease H IIb. Although the third largest subunit of calf thymus RNA polymerase I and ribonuclease H IIb display nearly identical molecular masses under denaturing conditions, serological analysis reveals that, in contrast to their counterparts in yeast, these mammalian proteins are distinct entities. Interestingly, sera from some patients with mixed connective tissue disease which contain antibodies directed against RNA polymerase I, also react with ribonuclease H IIb epitopes. This observation suggests that a protein displaying ribonuclease H IIb antigenicity could be associated with RNA polymerase I. Additional indications supporting this conclusion are discussed. 相似文献
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