Wot the 'L-Does MutL do?

In model DNA, A pairs with T, and C with G. However, in vivo, the complementarity of the DNA strands may be disrupted by errors in DNA replication, biochemical modification of bases and recombination. In prokaryotic organisms, mispaired bases are recognized by MutS homologs which, together with MutL homologs, initiate mismatch repair.

MutL: conducting the cell's response to mismatched and misaligned DNA.

Base pair mismatches in DNA arise from errors in DNA replication, recombination, and biochemical modification of bases. Mismatches are inherently transient. They are resolved passively by DNA replication, or actively by enzymatic removal and resynthesis of one of the bases.

Changes in the conformation of the Vsr endonuclease amino-terminal domain accompany DNA cleavage.

In Escherichia coli, T/G mismatches arising from deamination of 5-methylcytosine to thymine are converted to CG base pairs by the very short patch (VSP) repair pathway. DNA Polymerase I removes and resynthesizes the mismatched T starting from a 5'-nick created by the Vsr endonuclease. We used limited trypsinolysis to probe conformational changes in the N-terminal domain of Vsr in response to DNA binding, DNA cleavage and interaction with the polymerase.

The Escherichia coli mismatch repair protein MutL recruits the Vsr and MutH endonucleases in response to DNA damage.

The activities of the Vsr and MutH endonucleases of Escherichia coli are stimulated by MutL. The interaction of MutL with each enzyme is enhanced in vivo by 2-aminopurine treatment and by inactivation of the mutY gene. We hypothesize that MutL recruits the endonucleases to sites of DNA damage.

Interaction between the mismatch repair and nucleotide excision repair pathways in the prevention of 5-azacytidine-induced CG-to-GC mutations in Escherichia coli.

5-Azacytidine induces CG-to-GC transversion mutations in Escherichia coli. The results presented in this paper provide evidence that repair of the drug-induced lesions that produce these mutations involves components of both the mismatch repair and nucleotide excision repair systems. Strains deficient in mutL, mutS, uvrA, uvrB or uvrC all showed an increase in mutation in response to 5-azacytidine.

DNA polymerase lambda protects mouse fibroblasts against oxidative DNA damage and is recruited to sites of DNA damage/repair.

DNA polymerase lambda (pol lambda) is a member of the X family of DNA polymerases that has been implicated in both base excision repair and non-homologous end joining through in vitro studies. However, to date, no phenotype has been associated with cells deficient in this DNA polymerase. Here we show that pol lambda null mouse fibroblasts are hypersensitive to oxidative DNA damaging agents, suggesting a role of pol lambda in protection of cells against the cytotoxic effects of oxidized DNA.

'Knock down' of DNA polymerase beta by RNA interference: recapitulation of null phenotype.

DNA polymerase beta (pol beta) is the major DNA polymerase involved in the base excision repair (BER) pathway in mammalian cells and, as a consequence, BER is severely compromised in cells lacking pol beta. Pol beta null (-/-) mouse embryos are not viable and pol beta null cells are hypersensitive to alkylating agents. Using RNA interference (RNAi) technology in mouse cells, we have reduced the pol beta protein and mRNA to undetectable levels.

Stability of Natrialba magadii NDP kinase: comparisons with other halophilic proteins.

Nucleoside diphosphate kinase from the haloalkaliphilic archaeon Natrialba magadii (Nm NDPK) is a homooligomeric hexamer with a monomer molecular weight of 23 kDa. Its main function is to exchange gamma-phosphates between nucleoside triphosphates and diphosphates. Previously it was shown that Nm NDPK is active over a wide range of NaCl concentrations, which is not typical of extremely halophilic proteins.