The effect of the 3'-->5' exonuclease of T7 DNA polymerase on frameshifts and deletions.

Both spontaneous frameshift mutation and deletion mutation were measured in a T7 phage deficient in the 3'-->5' exonuclease of T7 DNA polymerase. It was found that the absence of this exonuclease caused a marked increase in the reversion of both plus one and minus one mutations. The exonuclease deficiency caused essentially no effect on the frequency of deletion between 10-bp direct repeats even when the segment between the direct repeats contained a 25-bp palindrome.