The FinO repressor of bacterial conjugation contains two RNA binding regions

Conjugative transfer of F-like plasmids in Escherichia coli is repressed by a plasmid-encoded protein, FinO. FinO blocks the translation of TraJ, a positive activator of transcription of genes required for conjugation. FinO binds a traJ antisense RNA, FinP, thereby protecting it from degradation, and catalyzes FinP-traJ mRNA hybridization. Interactions between these two RNAs are predicted to block the traJ ribosomal binding site. In this paper, we use limited proteolysis, circular dichroism spectroscopy, and an electrophoretic mobility shift assay to map the regions within FinO that are required for interactions with RNA. Our results show that FinO is largely helical, binds to its highest affinity binding site within FinP as a monomer, and contains two distinct RNA binding regions, one of which is localized between residues 26 and 61, and a second which is localized between residues 62 and 186.