Alcohol treatment of defective lambda lysogens is deletionogenic

We ascertained that transient exposure to ethanol, above 18%, was deletionogenic to an Escherichia coli strain with a fragment (12.5 kb) of bacteriophage lambda integrated within the chromosome. The lambda attL B.P' through P fragment provided a forward selection for mutants, and a target for mutagenesis. The cells were killed by thermal derepression of transcription and replication of the lambda fragment when transferred from 30 degrees to 42 degrees C. Survivor mutants, capable of forming colonies at 42 degrees C, were selected from untreated starting cells. About half no longer supported marker rescue of the lambda fragment imm lambda (immunity) region, comprising the cI repressor, and the PL and PR promoters. Ethanol treatment of starting cells increased the occurrence of imm lambda-defective clones to near 100%. The mutations responsible for the imm lambda defect were found to be large deletions (12 kb or more of DNA). Ethanol treatment of the starting cells also produced a 5- to 18-fold increase in the occurrence of E. coli pgl mutations, which likely arose by the deletion mechanism generating the imm lambda defects, since pgl was closely linked to the integrated lambda fragment. A unifying hypothesis for these observations was that ethanol was deletionogenic. The inclusion or substitution of the int-kil segment of the lambda fragment produced no real change in the spontaneous occurrence of large imm lambda deletions from the untreated cells. Substitution of this segment suppressed the deletionogenic effect of ethanol, implying a prerequisite for sequence homology or gene function from this interval.(ABSTRACT TRUNCATED AT 250 WORDS)