Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.31.1 (micrococcal nuclease)
 2,818 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have compared the nucleosomal organization of c-Ha-rasVal 12 oncogene-transformed NIH-3T3 fibroblasts with that of normal fibroblasts by using micrococcal nuclease (MNase) as a probe for the chromatin structure. The bulk chromatin from asynchronously and exponentially growing ras-transformed cells was much more sensitive to MNase digestion than chromatin from the normal cells. Southern hybridization analyses of the MNase digests with probes specific for the ornithine decarboxylase (odc) and c-myc genes showed that the coding and/or 3' end regions of these growth-inducible genes carry a nucleosomal organization both in ras-transformed and normal cells. Studies with cells synchronized by serum starvation showed that in both cell lines the nucleosomal organization of chromatin is relatively condensed at the quiescent state, becomes highly decondensed during the late G1 phase of the cell cycle, and starts again to condense during the S phase. However, in ras-transformed cells the decondensation state stayed much longer than in normal cells. Moreover, irrespective of the phase of the cell cycle the bulk chromatin as well as that of the odc and c-myc genes was more sensitive to MNase digestion in the ras-transformed cell than in the normal fibroblast. Decondensation of the chromatin was also observed in the normal c-Ha-ras protooncogene-transfected cells, but to a lesser extent than in the mutant ras-transformed cells. Whether the increased degree of chromatin decondensation plays a regulatory role in the increased expression of many growth-related genes in the ras-transformed cells remains an interesting object of further study.
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PMID:c-Ha-rasVal 12 oncogene-transformed NIH-3T3 fibroblasts display more decondensed nucleosomal organization than normal fibroblasts. 219 41

Treatment of calf thyroid slices with TSH increases the nuclease sensitivity of nuclear chromatin, i.e. the amount of DNA released from nuclei by mild digestion with DNase I and micrococcal nuclease. Cycloheximide and alpha-amanitin were used to investigate the roles played by protein and RNA synthesis in mediating this effect of TSH; alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, was used to investigate the possible involvement of polyamines. Calf thyroid slices were incubated with or without TSH (50 mU/ml) for 5 h, in the presence or absence of inhibitors. Nuclei were then prepared, subjected to mild digestion with micrococcal nuclease, and centrifuged at 1200 X g. The amount of DNA in 1200 X g supernatants was increased by TSH; this was inhibited by cycloheximide (100 micrograms/ml) and alpha-amanitin (4 micrograms/ml) when these agents were present throughout incubations with TSH. In contrast, alpha-amanitin failed to inhibit the TSH effect when it was added to incubations 30 min or 2 h after the addition of TSH. These results indicate that RNA and protein synthesis play a part in mediating the effect of TSH on the micrococcal nuclease sensitivity of chromatin, and that the RNA synthesis involved takes place within the first 30 min of exposure of thyroid slices to TSH. alpha-Difluoromethylornithine (5 mM) inhibited the TSH-dependent development of micrococcal nuclease sensitivity; however, it also inhibited nuclease digestion when it was added directly to nuclei prepared from fresh thyroid tissue. This observation should serve as a warning against uncritical acceptance of the notion that all effects of alpha-difluoromethylornithine are the result of inhibition of ornithine decarboxylase.
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PMID:Effects of cycloheximide, alpha-amanitin, and alpha-difluoromethylornithine on thyrotropin-induced increases in the micrococcal nuclease sensitivity of thyroid nuclear chromatin. 643 5

The early response gene ornithine decarboxylase (odc) is indispensable for normal and malignant cell growth. Although DNA methylation is generally associated with chromatin condensation and gene inactivation, the odc gene is heavily methylated at CCGG-sequences in animal cell lines. In this work we analyzed the chromatin structure and the DNA methylation status at the CpG-rich promoter sequences at the odc locus in mouse 3T3 fibroblasts. We show that the proximal promoter region of the odc locus is not hypermethylated, while the distal promoter sequences appear to have a few methylated CCGG-sites and display methylation polymorphism. Furthermore, it was found that the 5' promoter region of odc is constitutively more sensitive to micrococcal nuclease than the coding and 3' regions of the odc gene. Stimulation of the cells with serum resulted in an appearance of a DNase I sensitive site at the promoter region. The chromatin structure of the mid-coding and 3' regions of the odc gene also underwent structural changes that were accompanied by the rapid accumulation of odc mRNA. Such changes were not detected in the chromatin structure of glyceraldehyde-3-phosphate dehydrogenase (gadph) gene, whose expression remains invariant upon serum stimulation. These data suggest that the chromatin structure may play an important role in the rapid transcriptional activation of odc and other immediate early genes during serum stimulation.
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PMID:Methylation status and chromatin structure of an early response gene (ornithine decarboxylase) in resting and stimulated NIH-3T3 fibroblasts. 752 36

Several studies suggest that polyamines may stabilize chromatin and play a role in its structural alterations. In line with this idea, we found here by chromatin precipitation and micrococcal nuclease (MNase) digestion analyses, that spermidine and spermine stabilize or condense the nucleosomal organization of chromatin in vitro. We then investigated the possible physiological role of polyamines in the nucleosomal organization of chromatin during the cell cycle in Chinese hamster ovary (CHO) cells deficient in ornithine decarboxylase (ODC) activity. An extended polyamine deprivation (for 4 days) was found to arrest 70% of the odc- cells in S phase. MNase digestion analyses revealed that these cells have a highly loosened and destabilized nucleosomal organization. However, no marked difference in the chromatin structure was detected between the control and polyamine-depleted cells following the synchronization of the cells at the S-phase. We also show in synchronized cells that polyamine deprivation retards the traverse of the cells through the S phase already in the first cell cycle. Depletion of polyamines had no significant effect on the nucleosomal organization of chromatin in G1-early S. The polyamine-deprived cells were also capable of condensing the nucleosomal organization of chromatin in the S/G2 phase of the cell cycle. These data indicate that polyamines do not regulate the chromatin condensation state during the cell cycle, although they might have some stabilizing effect on the chromatin structure. Polyamines may, however, play an important role in the control of S-phase progression.
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PMID:Polyamines may regulate S-phase progression but not the dynamic changes of chromatin during the cell cycle. 944 76