Cooperation and competition in mismatch repair: very short-patch repair and methyl-directed mismatch repair in Escherichia coli.
In Escherichia coli and related enteric bacteria, repair of base-base mismatches is performed by two overlapping biochemical processes, methyl-directed mismatch repair (MMR) and very short-patch (VSP) repair. While MMR repairs replication errors, VSP repair corrects to C*G mispairs created by 5-methylcytosine deamination to T. The efficiency of the two pathways changes during the bacterial life cycle; MMR is more efficient during exponential growth and VSP repair is more efficient during the stationary phase. VSP repair and MMR share two proteins, MutS and MutL, and although the two repair pathways are not equally dependent on these proteins, their dual use creates a competition within the cells between the repair processes. The structural and biochemical data on the endonuclease that initiates VSP repair, Vsr, suggest that this protein plays a role similar to MutH (also an endonuclease) in MMR. Biochemical and genetic studies of the two repair pathways have helped eliminate certain models for MMR and put restrictions on models that can be developed regarding either repair process. We review here recent information about the biochemistry of both repair processes and describe the balancing act performed by cells to optimize the competing processes during different phases of the bacterial life cycle.
Bhagwat
Ashok S
AS
Department of Chemistry, Wayne State University, Detroit, MI 48202, USA. axb@chem.wayne.edu
Lieb
Margaret
M
D000225:Adenine / Q000378:metabolism; D000251:Adenosine Triphosphatases; D001426:Bacterial Proteins; D020137:Base Pair Mismatch; D019175:DNA Methylation; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D008958:Models, Molecular; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C074770:MutL protein, E coli; D004706:Endodeoxyribonucleases; C071421:vsr endonuclease; D000251:Adenosine Triphosphatases; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; C497175:MutS protein, E coli; D000225:Adenine