Gamma delta-mediated deletions of chromosomal segments on F-prime plasmids

Deleted derivatives of F lac+ proC+ tsx+/- purE+ plasmids ORF203 and F13 were isolated and physically characterized. Among 31 deletions, 24 were adjacent to the gamma delta element on F, four were associated with IS2 or IS3 elements normally present on F, and three displayed additional DNA rearrangements. With the genetic selection employed, the deletion endpoints in the chromosomal segment could fall anywhere within a 210 kb (5 min) region between proC and lac. The distribution of endpoints in this region was not random: the endpoints primarily occurred in an extended region near purE, and a 50 kb segment between tsx and purE was devoid of deletion endpoints. Deletion termini for mutants obtained from F13, which contains an additional 48 kb-segment interposed between gamma delta and the target region on ORF203, displayed a distribution similar to that seen for ORF203. Among simple deletions, there was no marked tendency for the chromosomal deletion endpoints to fall at IS1, IS3, or IS5 elements normally present in this chromosomal region. Point mutations and mutations caused by gamma delta or IS transposition into lac appeared in a small proportion of all plasmids studied.