Key Regulatory Aspects of Transfer of F-Related Plasmids

Current experiments designed to increase our understanding of the biochemistry of conjugation, as well as earlier experiments that mapped the transfer genes of the F sex factor, owe much of their design to the fact that transfer of the F sex factor is unregulated. Unregulated expression of transfer occurs because one of the critical regulatory genes of the transfer operon, the finO gene, was inactivated by the insertion of an IS3 sequence some time before F became a subject of study (6, 60). The existence of the moderately complex regulatory system in F transfer, to which this finO gene belongs, was first discovered by analysis of transfer of antibiotic resistance factors related to F (12, 54). In a series of elegant and insightful studies initially in the laboratory of Meynell (36, 37) and then in the laboratories of Anderson (la, 23, 46) and of Willetts (17–19), the basic control system for both F and related R factors such as R100 (also known as R222, NR1) was established several years ago. The final model proposed by Willetts (55) has stood against all challenges and is now generally accepted. A biological consequence of the “FinO-P” control system, as the model is now frequently called, is the subject of this chapter.