Isolation and characterization of high copy number suppressors of the SOS system in Escherichia coli

Abstract

In an attempt to find new genes that are involved in the induction of the SOS system of Escherichia coli, a plasmid library of Escherichia coli K-12 DNA cut with EcoRI was created in a pUC plasmid. The plasmids were transformed into the Escherichia coli strain AT492 containing a sulA::lacZ fusion. Colonies which did not show lacZ expression when the SOS systems had been induced by Mitomycin C were isolated. Four plasmids were found to suppress SOS induction when they were highly expressed. Kohara phage hybridization and restriction mapping suggest that these plasmids contain the genes for lexA and a truncated recA gene ending at the EcoRI site at basepair 1016.