Deletion between directly repeated DNA sequences measured in extracts of bacteriophage T7-infected Escherichia coli

An in vitro system based upon extracts of bacteriophage T7 infected Escherichia coli was used to study genetic deletions and to examine the importance of DNA replication in the deletion process. When T7 genomes with gene 1.3 inactivated by a 43-bp insert of random sequence DNA bracketed by 11-bp direct repeats were replicated in vitro the inserts were deleted with a frequency of about 10(-5) deletions per genome replication. Under conditions where deletion could take place only by recombination between direct repeats on distinct DNA molecules deletion frequency was at least an order of magnitude lower. These data demonstrate the utility of the in vitro system as a means for examining deletion mechanisms and underscore the importance of DNA replication in deletions.