POST-UV SURVIVAL OF ESCHERICHIA-COLI STRAINS CARRYING MORE THAN ONE UV-SENSITIZING PLASMID

The post-UV phenotypes conferred by wild-type plasmids R391 and pYD1, which increase UV-induced mutagenesis but sensitise Escherichia coli A B1157 umuC(+) uvrB(+) to UV, were compared, alone and in combination w ith that of plasmid pGW16, which sensitises AB1157 to low, but protect s against high UV doses. All three plasmids increased UV resistance wh en present in Shigella sonnei. No plasmid significantly affected the U V sensitivity of E. coli TK501 umuC uvrB, in which pKM101, the parent of pGW16 increases UV resistance up to 1000-fold. Both pYD1 and R391 r educed the UV protective effect of pKM101, and increased W-sensitisati on conferred by pGW16. W-sensitisation conferred by pYD1 and R391 was additive when the plasmids were together in strain AB1157, and both pK M101 and pGW16 reduced this additive sensitisation.