In UV-irradiatedEscherichia coli PQ35 overproducing the RecA protein, expression of thesfiA gene and dimer excision are alleviated

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Abstract
Escherichia coli PQ 35 cells carrying thesfiA-:lacZ operon fusion were transformed either with a multicopy plasmid containing therecA gene (pHSG262recA) or with a multicopy plasmid alone (pHSG262). Both transformants were UV irradiated. Then induction of thesfiA gene and dimer excision were followed. Amplification of therecA gene partly inhibited bothsfiA gene induction and dimer excision. The following interpretation of this phenomenon is proposed. When the RecA protein is in bundance, pyrimidine dimers are quickly masked by it. The masked dimers are less efficiently distinguished by excision nuclease and do not provide the induction signal. Due to this, induction of thesfiA gene as well as dimer excision are inhibited early.