Organization of transcribed regions of chromatin.
The endonuclease DNase II preferentially attacks a limited and tissue-specific portion of chromosomal DNA. This material may be separated from the bulk of chromatin DNA by virtue of its solubility in 2 mM MgCl2. The Mg2+ soluble fraction forms a specific subset of DNA sequences and is enriched four to sevenfold in sequences coding for cytoplasmic poly(A)-containing RNA and globin messenger RNA (in globin-producing cells). The bulk (70--90%) of rapidly labelled RNA is found associated with the Mg2+-soluble fraction. Transcriptionally active, Mc2+-soluble chromatin is organized into repeating subunits of DNA (200 +/- 5 base pairs) and histone. Mc2+-soluble active subunits differ from the subunits or nucleosomes of non-transcribed regions in many respects: namely, chemical composition (non-histone protein and RNA), sedimentation properties, differential sensitivity to DNase I and the single-strand-specific nuclease S1, and optical melting behaviour. These results suggest that chromatin subunits adopt a new configuration during the process of transcription.
D000818:Animals; D002843:Chromatin / Q000032:analysis / Q000235:genetics / Q000648:ultrastructure; D004247:DNA / Q000032:analysis; D003851:Deoxyribonucleases / Q000378:metabolism; D005796:Genes; D006657:Histones / Q000032:analysis; D008274:Magnesium / Q000494:pharmacology; D012313:RNA / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D014158:Transcription, Genetic
D002843:Chromatin; D006657:Histones; D012333:RNA, Messenger; D012313:RNA; D004247:DNA; D003851:Deoxyribonucleases; D008274:Magnesium