Analysis of the major domains of the F fertility inhibition protein, FinO.

The mechanism of fertility inhibition of conjugation by the F plasmid depends on the presence of both the FinO protein and an antisense RNA, FinP, which together control the expression of the positive regulator of the transfer operon TraJ. FinO both prevents the degradation of FinP, allowing its intracellular concentration to rise, and promotes duplex formation with its target, the traJ mRNA. In this study, deletions in finO were constructed and fused to gst, encoded by the pGEX-2T expression vector, to give GST-FinO fusions of varying lengths. These fusions were then tested for their ability to bind FinP and traJ mRNA, and to promote duplex formation. Our results suggest that the predicted basic N-terminal alpha-helix is involved in RNA binding, while the central domain is involved in duplex formation. The presence of the acidic C-terminal domain protects FinP from ribonucleolase degradation and might enhance binding of the N-terminal alpha-helical domain in a manner reminiscent of the Rom protein of ColE1.