Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The T5 D15 exonuclease purified from an overproducing strain of E. coli was shown to possess a low level of endonucleolytic activity specific for single-stranded DNA when assayed with 1-10 mM Mg2+ as co-factor. Endonuclease activity on double-stranded circular DNA could not be detected under these conditions. Nicked circular DNA was first gapped by the enzyme's exonucleolytic activity, creating a single-stranded region. This gapped substrate was then endonucleolytically cleaved and rapidly degraded. We show that a gapped and not a nicked substrate is required for this activity as previously suggested (Moyer, R. W. and Roth, C. T. 1977, J. Virol. 24, 177-193). The single-strand endonuclease activity could be selectively suppressed by using low concentrations of Mg2+ as co-factor (less than 1 mM), thus allowing nicked double-stranded circular DNA to be gapped to a single-stranded circular species. We also report on sequence similarities between the T5 exonuclease and several prokaryotic DNA polymerases.
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PMID:A single-strand specific endonuclease activity copurifies with overexpressed T5 D15 exonuclease. 165 77

In haploid rad52 Saccharomyces cerevisiae strains unable to undergo homologous recombination, a chromosomal double-strand break (DSB) can be repaired by imprecise rejoining of the broken chromosome ends. We have used two different strategies to generate broken chromosomes: (i) a site-specific DSB generated at the MAT locus by HO endonuclease cutting or (ii) a random DSB generated by mechanical rupture during mitotic segregation of a conditionally dicentric chromosome. Broken chromosomes were repaired by deletions that were highly variable in size, all of which removed more sequences than was required either to prevent subsequent HO cleavage or to eliminate a functional centromere, respectively. The junction of the deletions frequently occurred where complementary strands from the flanking DNA could anneal to form 1 to 5 bp, although 12% (4 of 34) of the events appear to have occurred by blunt-end ligation. These types of deletions are very similar to the junctions observed in the repair of DSBs by mammalian cells (D. B. Roth and J. H. Wilson, Mol. Cell. Biol. 6:4295-4304, 1986). When a high level of HO endonuclease, expressed in all phases of the cell cycle, was used to create DSBs, we also recovered a large class of very small (2- or 3-bp) insertions in the HO cleavage site. These insertions appear to represent still another mechanism of DSB repair, apparently by annealing and filling in the overhanging 3' ends of the cleavage site. These types of events have also been well documented for vertebrate cells.
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PMID:Two different types of double-strand breaks in Saccharomyces cerevisiae are repaired by similar RAD52-independent, nonhomologous recombination events. 828 8

During B and T lymphocyte development, immunoglobulin and T cell receptor genes are assembled from the germline V, (D) and J gene segments (Lewis, S.M., 1994. The mechanism of V(D)J joining: lessons from molecular, immunological and comparative analyses. Adv. Immunol. 56, 27-150). These DNA rearrangements, responsible for immune system diversity, are mediated by a site specific recombination machinery via recognition signal sequences (RSSs) composed of conserved heptamers and nonamers separated by spacers of 12 or 23 nucleotides (Lewis, S.M., 1994. The mechanism of V(D)J joining: lessons from molecular, immunological and comparative analyses. Adv. Immunol. 56, 27-150). Recombination occurs only between a RSS with a 12mer spacer and a RSS with a 23mer spacer (Lewis, S.M., 1994. The mechanism of V(D)J joining: lessons from molecular, immunological and comparative analyses. Adv. Immunol. 56, 27-150). RAG1 and RAG2 proteins cleave precisely at the RSS-coding sequence border leading to flush signal ends and coding ends with a hairpin structure (Eastman, M., Leu, T., Schatz, D., 1996. Initiation of V(D)J recombination in vitro obeying the 12/23 rule. Nature 380, 85-88; Roth, D.B., Menetski, J.P., Nakajima, P.B., Bosma, M.J., Gellert, M., 1992. V(D)J recombination: broken DNA molecules with covalently sealed (hairpin) coding ends in scid mouse thymocytes. Cell 983-991: Roth, D.B., Zhu, C., Gellert. M., 1993. Characterization of broken DNA molecules associated with V(D)J recombination. Proc. Natl. Acad. Sci. USA 90, 10,788-10,792; van Gent, D., McBlane, J.. Sadofsky, M., Hesse, J., Gellert, M., 1995. Initiation of V(D)J recombination in a cell-free system. Cell 81, 925-934). Signal ends join, forming a signal joint. The hairpin coding ends are opened by a yet unknown endonuclease, and are further processed to form the coding joint (Lewis, S.M., 1994. The mechanism of V(D)J joining: lessons from molecular, immunological and comparative analyses. Ad. Immunol. 56, 27-150.) The murine scid mutation has been shown to affect coding joints, but much less signal joint formation. In this study we demonstrate that the murine scid mutation inhibits correct signal joint formation when both coding ends contain homopolymeric sequences. We suggest that this finding may be due to the function of the SCID protein as an assembly component in V(D)J recombination.
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PMID:Signal joint formation is inhibited in murine scid preB cells and fibroblasts in substrates with homopolymeric coding ends. 1047 10