Specific Chromosomal Affinity of a Resistance Factor

SUMMARY R factors, responsible for transmissible drug resistance in Enterobacteriaceae, convert their hosts into donors of genetic material, but fewer recombinants for chromosomal genes are produced than with F. For one R factor, at least, this was merely a consequence of less frequent conjugation. With a mutant where conjugation was not repressed in contrast to the wild type, this R factor, R 1, was shown to behave like an F′ factor and to transfer the bacterial chromosome at high frequency from a fixed origin near the try genes.