The nature and incidence of conjugation factors inEscherichia coli

The sex factor F is itself exceptional among conjugation factors in being freely expressed in all the bacteria of a culture, while related factors which are largely unexpressed are widespread. These can be recognized by the presence of a small proportion of cells sensitive to phage specific for F+bacteria, and may sometimes constitute the conjugation factors associated with colicinogeny. Moreover, F itself can mutate to the repressed state so that derivatives ofE. coliK12 which appear F−include some in which F is still present but rarely expressed.