[Further genetic study of tandem duplication formation in the region of the deo operon in the process of Escherichia coli K-12 conjugational recombination].

The formation of heterozygous duplications in the region of the deo operon was studied in conjugational matings (male) HfrH deoC deoD thr::Tn9 thyA x HfrH deoA deoB::Tn5 thyA. When recombinants that inherited the donor marker thr::Tn9 (Cml r) were selected on a medium containing thymine and chloramphenicol, but not threonine, more than 80% of the offspring were heterozygous tandem duplications extending to the region of the deo operon. In matings with a thymidine-dependent HfrH deoA deoB::Tn5 thyA strain as a recipient, when recombinants were selected on a medium containing thymine, i.e., under conditions of thymine starvation of merozygotes, the recombinogenic effect was observed. However, this effect did not change the frequency of duplication formation. The integration of genetic markers via homologous recombination into the chromosomal regions adjacent to duplications occurred at a lower frequency. An analysis of the formation of haploid segregants by duplications showed that, in most cases of duplication formation, the proximal segment of the donor chromosome is integrated into the distal position, i.e., after the homologous segment of the recipient chromosome.