Plasmid pKM101-mediated mutagenesis in Escherichia coli is inducible.

A tif-1 umuC36 double mutant of Escherichia coli was constructed. It has been found that the umuC36 mutation prevents both increased spontaneous mutagenesis and enhanced reactivation of UV-irradiated lambda, phenomena normally observed in the tif-1 strain grown at 42 degrees C. When the plasmid pKM101 was introduced into tif-1 umuC36, an elevated spontaneous reversion rate of the his-4 mutation observed at 30 degrees C was further increased 6-fold at 42 degrees C. This was accompanied by a 10-fold increase in the ability of tif-1 umuC36 containing pKM101 and grown before infection at 42 degrees C to reactivate UV-irradiated lambda.