An extrachromosomal factor, colicinogenic factor B (colB) inhibits expression of fertility functions of various F-type factors in strains of E. coli K12. Mutant F-lac factors simultaneously became insensitive to all the effects of colB as well as to similar actions exerted by a resistance transfer factor, R fi(+). This suggests that a common site or activity necessary for the expression of several F functions is affected by products of both colB and R fi(+).
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Negrotti et al. (1972) studied this question.
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