Are adaptive mutations due to a decline in mismatch repair? The evidence is lacking.

The levels of proteins required for methyl-directed mismatch repair appear to decline in stationary-phase and nutritionally-deprived cells of Escherichia coli. It has been hypothesized that error-correction by the system also declines, and this decline is responsible for adaptive or stationary-phase mutations. However, evidence in support of this hypothesis is lacking. The mismatch repair system is no less effective in correcting errors during prolonged selection than it is during growth. Furthermore, mismatch repair proteins supplied in excess reduce both growth-dependent and adaptive mutation. Copyright 1999 Elsevier Science B.V.