Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The structure of the chicken adult beta-globin gene chromatin in immature and mature erythrocyte nuclei has been analysed using micrococcal nuclease digestion. The resulting DNA fragments were blotted onto DBM-papers and probed with labelled DNA fragments spanning the adult beta-globin gene and its 5'- and 3'-flanking regions. The structure of the nucleosomes within and in the regions flanking the adult beta-globin gene appears to be altered in at least two ways in erythrocyte chromatin, when compared with either bulk or inactive ovalbumin gene chromatin. First, oligomeric DNA fragments containing the beta-globin gene are released faster than those of either bulk or ovalbumin gene chromatin. Second, although the difference in size of the liberated oligomeric DNA fragments is similar to the nucleosomal repeat length of bulk and ovalbumin gene chromatin, the individual oligomers are approximately 100 bp shorter than their bulk or ovalbumin gene counterparts, most noticeably when the nuclease digestion is performed at 37 degrees C. This results in an atypical ladder of approximately 300, 500, 700, 900 bp instead of the canonical chicken erythrocyte ladder which is an integral multiple of 207 bp. The same ladder was obtained from immature erythrocytes, in which the beta-globin gene is actively transcribed, and from mature erythrocytes, in which it is considered to be inactive with RNA polymerase molecules clustered in the 5' moiety of the gene. This indicates that the alteration of the nucleosomal structure is not due to transcription per se.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Digestion of the chicken beta-globin gene chromatin with micrococcal nuclease reveals the presence of an altered nucleosomal array characterized by an atypical ladder of DNA fragments. 301

The ribosomal genes of Dictyostelium discoideum are extrachromosomal palindromic DNA molecules situated in the nucleolus. Each molecule comprises ribosomal RNA coding regions and non-transcribed spacer regions. We used both biochemical and electron microscopic approaches to investigate the structure of transcribing and non-transcribing chromatin. Nucleoli from exponentially growing cells were digested with micrococcal nuclease, and the resulting DNA fragments were separated by gel electrophoresis and transferred to DBM paper. They were hybridized with cloned EcoRI fragments derived from different parts of the ribosomal gene. Probes of the coding region showed a smear, while probes of the non-transcribed regions gave pronounced banding patterns more complex than typical nucleosome repeats, but not due solely to sequence-specific cutting by micrococcal nuclease. The DNA of the coding region was digested more quickly than that of the non-transcribed ones. When nucleoli were digested with restriction enzymes, sites within the coding region were accessible and sites in the non-transcribed region were protected. The structure of ribosomal chromatin in differentiating cells, in which the rate of ribosomal RNA synthesis is reduced, was examined using essentially the same methods. The coding region, probed by hybridization to micrococcal digests, then showed a typical DNA repeat pattern indicating that this region had become condensed into nucleosomes, and its accessibility to restriction enzymes was very much reduced. On electron micrographs of lysed nucleoli from exponentially growing cells, two types of chromatin were observed, one with a beaded nucleosomal appearance, the other with putative RNA polymerase molecules attached to fibres indistinguishable from free DNA adsorbed to the same grid. The combined results suggest that whereas regions that are not transcribed are packaged with proteins that protect them from nuclease digestion, actively transcribing ribosomal genes are associated with few macromolecular constituents apart from those required for transcription and its regulation.
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PMID:Chromatin structure along the ribosomal DNA of Dictyostelium. Regional differences and changes accompanying cell differentiation. 630 25