Dominance study with rifampicin-resistant mutants of E. coli K 12

Summary The location of the characters for rifampicin-resistance in E. coli linked to the arg E marker was confirmed by mating experiments with rifampicin-resistant Hfr C mutants and a rifampicin-sensitive acceptor strain. During these tests, temporary dominance of rifampicin-sensitivity was observed. On the basis of the results obtained, the time required for complete phenotypic expression of rifampicin-resistance was determined, and the ratios of rifampicin-sensitivity to rifampicin-resistance in the merozygote phase of the cell were studied. It was found that the episomal marker of rifampicin-sensitivity influences the level of resistance in merodiploid cells, but does not fully restore the original sensitivity of the wild type.