Mutagenic repair in Escherichia coli. X. The umuC gene product may be required for replication past pyrimidine dimers but not for the coding error in UV-mutagenesis.

Bacteria of strain TK610 uvrA-6 his-4 umuC-36, when allowed to replicate their DNA for some hours after irradiation show induction of His+ mutations when subsequently exposed to visible light. It is suggested that base pair errors can be made opposite sites of pyrimidine dimers without involvement of umuC gene product but that the latter is required for continued replication past the dimer-mismatch region. Removal of the pyrimidine dimer by photoreversal allows replication to continue thus fixing the mismatched base as as mutation.