The SoS response

Should the base pairing between strands still remain incorrect, the Bacterial cell has a final mechanism to excise corrupted DNA. This mechanism may actually result in the persistence of mutations in the next generation but prevents the accumulation of mismatches to the point where they become lethal. Normally a protein called LexA represses an overall response, but as mismatches accumulate, the concentration of another protein RecA also rises. A high concentration of RecA causes the cleavage of LexA. In the absence of LexA, 17 genes are turned on which constitute the SOS response. This system quickly resolves all DNA mismatches, but does not distinguish between parental and daughter strands. The cell can continue replication, but this response is extremely error-prone.