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.