Evidence of photoenzymatic repair due to the phrA gene in a phrB mutant of Escherichia coli K-12.

The role of the phrA gene in the genetic control of photoreactivation in Escherichia coli has been a matter of some controversy. It has been proposed that the gene has no significant physiological role in photoreactivation. However, we have previously sequenced a restriction fragment thought to contain the phrA gene and shown it to contain a putative gene. When this gene, termed the putative phrA gene, was transformed into a phrAphrB mutant, a photoreactivable response above that of the phrAphrB mutant was observed. It has been suggested that the photorepair seen in phrB mutants is due to Type III photoreactivation, which is independent of temperature and fluence rate effects. Here we have shown that the photorecovery associated with the phrA gene is dependent on both temperature and fluence rate. This suggests that the photorecovery is not due to Type III photoreactivation but to an enzymatic reaction caused by an unknown photoactive protein, the phrA gene product, which acts on lesions other than pyrimidine dimers, possibly pyrimidine (6-4) pyrimidone photoproducts. We therefore propose that the phrA gene be reaccepted and its role in photoreactivation in Escherichia coli acknowledged.