Mutagenesis induced by site specifically placed 4'-hydroxymethyl-4,5',8-trimethylpsoralen adducts

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Abstract
Closed circular double stranded M13mp19 DNA containing a site-specifically placed HMT (4''-hydroxymethyl-4-5''-8-trimethylpsoralen) monoadduct or crosslink was synthesized in vitro. The damaged DNA were scored for loss of infectivity by transfection into repair proficient or deficient Escherichia coli and into SOS induced E. coli. Mutant phages were detected by the loss of .alpha.-complementation between the viral and the host Lac Z genes or by the acquisition of resistance to kpm I digestion. Our results indicate that HMT mutagenesis is targeted and that deletion or transversion of the modified thymidine is the predominant sequence change elicited by a monoadduct or a crosslink. Transfection of the monoadducted DNA into a Uvr A deficient strain did not change the mutation pattern but did increase the respective mutation frequencies. Transfection of the crosslinked DNA into a SOS induced host resulted in the appearance of other types of mutations attribuable to an increase in both targeted and untargeted mutations.