FIG. 1.
The F-plasmid regulatory circuit is composed of three major plasmid-encoded regulatory proteins: TraJ, TraY, and TraM. TraJ is the primary activator and appears to act by countering repression by the host factor, H-NS, at the tra operon promoter PY. TraY also activates the tra gene at PY, as well as the traM promoter, PM. TraM and TraY act as autorepressors at their respective promoters, with TraY also having a role as an activator in exponential phase. Most F-like plasmids are also regulated by the FinOP antisense RNA system, where an antisense RNA, FinP, complementary to the 5′ UTR of traJ, forms a duplex with that transcript and sequesters the traJ RBS. FinO, an RNA chaperone encoded by the plasmid, is necessary to stabilize FinP and promote duplex formation. However, finO is disrupted in the F plasmid, resulting in the derepression of tra gene expression.