Study of the expression of UVRA and SSB proteins in vivo in λ hybrid phages containing the uvrA and ssbA genes of Escherichia coli

Abstract

A 9.3-kb Eco RI fragment obtained by partial digestion of the plasmid pDR2000 and containing the uvrA and ssbA genes was subcloned in the insertion vector λ gt4. Two hybrid bacteriophages carrying this fragment inserted in opposite orientations were isolated and used to lysogenize a uvrA and an ssbA mutant of Escherichia coli. Both phages confered to these host bacteria the ultraviolet resistance of the wild-type parent indicating full complementation of the uvrA and of the ssbA defect. Two polypeptides corresponding to the molecular weights of the UVRA protein (115 000 dalton) and of the SSB protein (18 500 dalton) were synthesized and amplified after infection of a UV-irradiated λ ind − lysogen with these 2 hybrid phages. The UVRA protein was not amplified after infection of a lex A3 host while SSB was still produced in large amount. These results establish that uvrA is repressed by lexA in vivo whereas ssbA is not.