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)

To improve our understanding of the mechanism of 1-beta-D-arabinofuranosylcytosine (ara-C) incorporation into DNA, we investigated the physical properties (size, position of nucleoside incorporation) of small fragments of nascent DNA (nDNA) obtained by pH-step alkaline elution of intact HL-60 cells following their exposure to ara-C. In the pH-step alkaline elution procedure, the smallest fragments of nDNA elute at pH 11. Anion-exchange high-performance liquid chromatography (HPLC) of nDNA obtained by 1 h elution at pH 11.0 of lysed HL-60 cells revealed a preponderance of nDNA fragments ranging from 0.5 to 40 kb in control ([3H]-dThd-labeled) cells. Exposure of cells to ara-C (0.8-1 microM) resulted in a loss of the preponderance of radiolabel in fragments of 0.5-40 kb along with redistribution of the radiolabel (from [3H]-dThd or [3H]-ara-C) into smaller nDNA fragments (predominantly < 100 bases in length) as determined by HPLC. We used the ability of pH-step alkaline elution to provide these small nDNA fragments produced by ara-C to investigate the paradoxical behavior of ara-C as a chain terminator in cell-free DNA synthetic systems while being incorporated into an internucleotide position in intact cells. Following the digestion of purified nDNA with micrococcal nuclease and spleen phosphodiesterase II, the proportion of radiolabel in 3'-dNMP (indicating an internucleotide position) or free nucleoside (indicating a chain terminus position) was determined by reverse-phase HPLC. In digests of prelabeled genomic DNA, as expected, > 90% of the radiolabel from [14C]-dThd or [3H]-ara-C was found to exist in an internucleotide position (as determined by co-chromatography with authentic 3'-dTMP or 3'-ara-CMP). In contrast, digests of nDNA that eluted at pH 11.0 revealed a significantly higher proportion of radiolabel in the chain terminus position (29%-35%) when the nDNA was obtained from cells exposed to 1 microM [3H]-ara-C as compared with cells exposed to [3H]-dThd or [3H]-dCyd alone (< 10%). These data obtained from pH-step alkaline elution of intact cells suggest that by causing the inhibition of chain elongation while failing to inhibit the formation of new nDNA replication intermediates, ara-C exposure leads to the production of very small nDNA fragments. This relative chain-terminating effect of ara-C is most apparent in the small nDNA replication fragments that elute at pH 11.0.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mechanistic implications of alterations in HL-60 cell nascent DNA after exposure to 1-beta-D-arabinofuranosylcytosine. 145 61

A ribonucleoprotein (RNP) particle sedimenting at 10 S in sucrose gradients had been isolated from the post-polysomal fraction of homogenates of 14-day-old chick embryonic leg and breast muscle by sucrose gradient fractionation and gel filtration. The 10 S RNP contains a 4 S RNA species (base composition: AMP, .3%; GMP, 22.2%; CMP, 24.2%; and UMP, 23.2%), and shows three major bands in the 70-90-nucleotide size range by polyacrylamide gel electrophoresis in 99% formamide. The 4 S RNA does not contain oligo(U)- and oligo(A)-rich tracts. The RNP has a characteristic buoyant density of 1.410 g/ml, which corresponds to an RNA/protein ratio of about 1:4. The UV absorption spectra of the RNP is very distinct from that of its RNA component. Both 4 S RNA and the 10 S RNP are potent inhibitors of translation of a variety of mRNAs such as chick muscle poly(A)+ mRNA, rabbit globin mRNA, EMC virus RNA, and poly(A)- and mRNA of rat liver in micrococcal nuclease-treated rabbit reticulocyte lysate. The inhibitory action of the RNA and the RNP on mRNA translation appears to involve the initiation process. The RNA and RNP do not have a nuclease activity associated with them. The hyperchromicity profile of the inhibitory RNA with increasing temperature indicates that it does not contain a significant amount of double-stranded structure. This is also supported by the complete loss of biological activity of the RNA by treatment with pancreatic RNase. In contrast, the inhibitory activity of the RNP was resistant to RNase. Electrophoresis of the protein moieties of the inhibitory RNP using both one- and two-dimensional gel techniques in the presence of sodium dodecyl sulfate shows a complex pattern of polypeptides of Mr = 12,000-150,000. The protein pattern of the 10 S particle is quite different from those of free and polysomal mRNP and poly(A)-protein complexes of chick embryonic muscles, indicating that most, if not all of the mRNA-associated proteins, are absent in the 19 S RNP. The properties of the inhibitory RNA indicate that it is different from the various low molecular weight RNA species which are involved in the modulation of protein synthesis in cell-free systems. It is concluded that the 10 S particle represents a novel class of RNP, which may be involved in posttranscriptional regulation of protein synthesis in embryonic muscles.
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PMID:A ribonuclease-resistant cytoplasmic 10 S ribonucleoprotein of chick embryonic muscle. A potent inhibitor of cell-free protein synthesis. 611 23