STRUCTURE OF RECOMBINANTS FROM CONJUGATIONAL CROSSES BETWEEN ESCHERICHIA-COLI DONOR AND MISMATCH-REPAIR DEFICIENT SALMONELLA-TYPHIMURIUM RECIPIENTS

To get more insight into the control of homologous recombination betwe en diverged DNA by the Mut proteins of the long-patch mismatch repair system, we have studied interspecies Escherichia coli/Salmonella typhi murium recombination. Knowing that the same recombination pathway (Rec ABCD) is responsible for intraspecies and interspecies recombination, we have now studied the structure (replacement vs. addition-type or ot her rearrangement-type recombinants) of 81 interspecies recombinants o btained in conjugational crosses between E. coli donor and mutL, mutS, mutH, mutU or mut+ S. typhimurium recipients. Taking advantage of hig h interspecies sequence divergence, a physical analysis was performed on one third of the E. coli Hfr genome, which was expected to be trans ferred to S. typhimurium F- recipients during 40 min before interrupti on of the mating. Probes specific for each species were hybridized on dot blots of genomic DNA, or on colonies, and the composition of the r rn operons was determined from purified genomic DNA. With very few exc eptions, the structure of these interspecies recombinants corresponds to replacements of one continuous block of the recipient genome by the corresponding region of the donor genome.