This family includes ProQ, which is required for full activation of the osmoprotectant transporter, ProP, in Escherichia coli. This family includes several bacterial fertility inhibition (FINO) proteins. The conjugative transfer of F-like plasmids is repressed by FinO, an RNA binding protein. FinO interacts with the F-plasmid encoded traJ mRNA and its antisense RNA, FinP, stabilising FinP against endonucleolytic degradation and facilitating sense-antisense RNA recognition [2]. ProQ operates as an RNA-chaperone, binding RNA and bringing about both RNA strand-exchange and RNA duplexing. This suggests that in fact it does not regulate ProP transcription but rather regulates ProP translation through activity as an RNA-binding protein [3].

1: Protein ProQ influences osmotic activation of compatible solute transporter ProP in Escherichia coli K-12. Kunte HJ, Crane RA, Culham DE, Richmond D, Wood JM; J Bacteriol 1999;181:1537-1543. PMID:10049386

2: Crystal structure of the bacterial conjugation repressor finO. Ghetu AF, Gubbins MJ, Frost LS, Glover JN; Nat Struct Biol 2000;7:565-569. PMID:10876242

3: ProQ is an RNA chaperone that controls ProP levels in Escherichia coli. Chaulk SG, Smith Frieday MN, Arthur DC, Culham DE, Edwards RA, Soo P, Frost LS, Keates RA, Glover JN, Wood JM; Biochemistry. 2011;50:3095-3106. PMID:21381725