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Query: UMLS:C1389183 (autodigestion)
 317 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The nucleosomes released by the incubation (autodigestion) of rat-liver nuclei were fractionated by sucrose-density gradient centrifugation, and subjected to nuclease assay with heat-denatured 3H-DNA from Escherichia coli as an exogenous substrate. With increasing incubation time, the nuclease activity was enhanced and localized in the mono/tetra-, hexa/hepta-, and long-chain oligonucleosome fractions. In contrast, independent of the nucleosome size, the activities of 0.35 M NaCl-soluble fractions from them were found to be almost equal in terms of specific activity (dpm/nucleosomal DNA). Such nuclease activity was not detected in the sucrose gradient (top region) lacking nucleosomes and/or chromatin. When the chromatin was dialyzed against a 0.35 M NaCl buffer and then fractionated in a sucrose gradient containing 0.35 M NaCl, most of the nuclease activity was solubilized into the above top region. On gel filtration of the mononucleosome fraction in the 0.35 M NaCl buffer, the nuclease activity was eluted at the position of 36,000 daltons. This nuclease cleaved heat-denatured DNA more rapidly than the native DNA in the presence of Mg2+, and had the ability to make both single-strand nicks and double-strand cuts in pBR322 DNA; in other words, it had an endonucleolytic activity. Moreover, four different classes of mononucleosomes were fractionated by electrophoresis of the nucleosomes released by autodigestion of the nuclei. These mononucleosomes also showed nuclease activity with the heat-denatured DNA. Thus, the present studies suggest that an Mg2+-dependent endonuclease of about 36,000 daltons is associated with the nucleosome particle(s) in rat-liver nuclei.
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PMID:The association of a magnesium-dependent endonuclease activity with a nucleosome fraction from rat-liver nuclei. 409 46

Proteolytic cleavage of lexA repressor is an early step in derepression of the SOS regulatory system of Escherichia coli. In vivo and in vitro data have indicated a role for recA protein in this specific proteolytic reaction. I show here that, under certain conditions, specific in vitro cleavage of highly-purified lexA protein can take place in the absence of recA protein. This autodigestion reaction cleaved the same alanine-glycine bond as did the recA-dependent cleavage reaction. Several lines of evidence argued that it was not due to a contaminating protease activity. Autodigestion was stimulated by alkaline pH. It occurred in the presence of EDTA but was stimulated several fold by the presence of Ca2+, Co2+, or Mg2+. The reaction appeared to be first-order, and its rate was independent of protein concentration over a wide range, strongly suggesting that it is intramolecular. Purified phage lambda repressor also broke down under similar conditions to yield products like those resulting from recA protein action. Phage lambda repressor broke down at a far slower rate than did lexA, as previously observed in the recA-catalyzed in vitro reaction and in vivo. This correlation between the two types of cleavage also extended to the reactions with mutant repressor proteins; taken together with the site specificity, it suggests that autodigestion and recA-dependent cleavage follow, at least in part, a similar reaction pathway. These findings indicate that specific cleavage of lexA protein can be catalyzed by the protein itself and suggest that recA protein plays an indirect stimulatory role, perhaps as an allosteric effector, in the recA-dependent reaction, rather than acting directly as a protease. The protease active site and the recA-recognition site lie in the central or COOH-terminal portion of the lexA protein, since a tryptic fragment containing these portions of lexA protein could take part in both reactions.
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PMID:Autodigestion of lexA and phage lambda repressors. 623 41

Using an autodigestion method, we investigated endogenous endonuclease(s) in leukemia cells freshly obtained from pediatric patients with various types of leukemia. Endonucleolytic activity was found to cause both high molecular weight and internucleosomal DNA fragmentation at a neutral pH in whole cell lysates of all common acute lymphoblastic leukemia (cALL) blasts, which was Mg2+-dependent and Ca2+-independent. Whole lysates from most acute myeloblastic leukemia (AML) cells possessed similar endonuclease activity, but both Mg2+ and Ca2+ were required for the activity. Our results suggest that leukemia cells of different lineages have distinct constitutive endonucleases, which may play a role in the occurrence of apoptosis in these cells.
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PMID:Constitutive endonuclease to induce high molecular weight or internucleosomal DNA fragmentation in freshly isolated leukemia cells. 923 28