UNEQUAL CROSSING-OVER IN ESCHERICHIA-COLI - GENETIC AND PHYSICAL MAPPING OF DUPLICATIONS ISOLATED IN CONJUGATIONAL MATINGS

We previously demonstrated that stable heterozygous duplications deoA deoB :: Tn5/deoC deoD can be isolated among Deo(+) recombinants obtain ed in conjugational matings between Escherichia toll strains HfrH deoA deoB :: Tn5 and Hfr-H deoC deoD. In this work, 30 duplications were t ested by transduction for the inclusion of a set of the genetic marker s adjoining the deo operon (99.5 min) at the genetic map of E. coli: c ycA :: Tn10 (96 min), zji :: Tn10 (98.2 min), thr :: Tn9 (100/0 min), car :: Tn10 (1 min), leu :: Tn9 (2 min), and proAB :: Tn10 (6 min). Th e results obtained indicate that only three out of 30 duplications cou ld have originated from unequal crossing over between the rm operons. In eight strains, duplications were chosen for physical mapping by the use of Not I restriction, pulsed-field electrophoresis, and Southern blot hybridization with DNA of the deo operon. In all these strains, t he presence of duplications (once a triplication) was confirmed by cor responding changes in the set of Not I digests, although some strains had additional genetic rearrangements. The order of operon copies in a tandem was determined, and the length of a duplicated chromosomal seg ment was calculated as equal to 25, 46, 80, 150.5, and 175 kb in dupli cations D49, D4, D5, D9, and D18, respectively. Thus, the use of the c onjugational Hfr x Hfr system allows the generation of unique rearrang ements of the E. coli genetic material.