Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.5.1.2 (DNA ligase)
 2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The establishment of sister chromatid cohesion during S phase and its dissolution at the metaphase-anaphase transition are essential for the faithful segregation of chromosomes in mitosis [1-4]. Recent studies in yeast genetics and Xenopus biochemistry have identified a large protein complex, cohesin, that plays a key role in sister chromatid cohesion [5-10]. The cohesin complex consists of a heterodimeric pair of SMC (structural maintenance of chromosomes) subunits and at least two non-SMC subunits. This structural organization is reminiscent of that of condensin, another major SMC protein complex that drives chromosome condensation in eukaryotic cells [11]. Condensin has been shown to reconfigure and compact DNA in vitro by utilizing the energy of ATP hydrolysis [12]. Very little is known, however, about how cohesin works at a mechanistic level. Here we report the first set of biochemical activities associated with an intact cohesin complex purified from HeLa cell extracts. The cohesin complex binds directly to double-stranded DNA and induces the formation of large protein-DNA aggregates. In the presence of topoisomerase II, cohesin stimulates intermolecular catenation of circular DNA molecules. This activity is in striking contrast to intramolecular knotting directed by condensin [13]. Cohesin also increases the probability of intermolecular ligation of linear DNA molecules in the presence of DNA ligase. Our results are consistent with a model in which cohesin functions as an intermolecular DNA crosslinker and is part of the molecular "glue" that holds sister chromatids together [14].
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PMID:Intermolecular DNA interactions stimulated by the cohesin complex in vitro: implications for sister chromatid cohesion. 1125 Jan 56

Smc2/4 forms the core of the Saccharomyces cerevisiae condensin, which promotes metaphase chromosome compaction. To understand how condensin manipulates DNA, we used two in vitro assays to study the role of SMC (structural maintenance of chromosome) proteins and ATP in reconfiguring the path of DNA. The first assay evaluated the topology of knots formed in the presence of topoisomerase II. Unexpectedly, both wild-type Smc2/4 and an ATPase mutant promoted (+) chiral knotting of nicked plasmids, revealing that ATP hydrolysis and the non-SMC condensins are not required to compact DNA chirally. The second assay measured Smc2/4-dependent changes in linking number (Lk). Smc2/4 did not induce (+) supercoiling, but instead induced broadening of topoisomer distributions in a cooperative manner without altering Lk(0). To explain chiral knotting in substrates devoid of chiral supercoiling, we propose that Smc2/4 directs chiral DNA compaction by constraining the duplex to retrace its own path. In this highly cooperative process, both (+) and (-) loops are sequestered (about one per kb), leaving net writhe and twist unchanged while broadening Lk. We have developed a quantitative theory to account for these results. Additionally, we have shown at higher molar stoichiometries that Smc2/4 prevents relaxation by topoisomerase I and nick closure by DNA ligase, indicating that Smc2/4 can saturate DNA. By electron microscopy of Smc2/4-DNA complexes, we observed primarily two protein-laden bound species: long flexible filaments and uniform rings or "doughnuts." Close packing of Smc2/4 on DNA explains the substrate protection we observed. Our results support the hypothesis that SMC proteins bind multiple DNA duplexes.
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PMID:The Saccharomyces cerevisiae Smc2/4 condensin compacts DNA into (+) chiral structures without net supercoiling. 1610 Jan 11

The bacterial RecN protein is involved in the recombinational repair of DNA double-stranded breaks, and recN mutants are sensitive to DNA-damaging agents. Little is known about the biochemical function of RecN. Protein sequence analysis suggests that RecN is related to the SMC (structural maintenance of chromosomes) family of proteins, predicting globular N- and C-terminal domains connected by an extensive coil-coiled domain. The N- and C-domains contain the nucleotide-binding sequences Walker A and Walker B, respectively. We have purified the RecN protein from Deinococcus radiodurans and characterized its DNA-dependent and DNA-independent ATPase activity. The RecN protein hydrolyzes ATP with a k(cat) of 24 min(-1), and this rate is stimulated 4-fold by duplex DNA but not by single-stranded DNA. This DNA-dependent ATP turnover rate exhibits a dependence on the concentration of RecN protein, suggesting that RecN-RecN interactions are required for efficient ATP hydrolysis, and those interactions are stabilized only by duplex DNA. Finally, we show that RecN stimulates the intermolecular ligation of linear DNA molecules in the presence of DNA ligase. This DNA bridging activity is strikingly similar to that of the cohesin complex, an SMC family member, to which RecN is related.
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PMID:RecN is a cohesin-like protein that stimulates intermolecular DNA interactions in vitro. 2036 8