The FinO family of bacterial RNA chaperones J.N. Mark Glover a, *, Steven G. Chaulk a , Ross A. Edwards a , David Arthur a , Jun Lu a , Laura S. Frost b a Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada b Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada A R T I C L E I N FO Article history: Available online 4 August 2014 Communicated by Ananda Chakrabarty Keywords: FinO FinP Antisense RNA RNA chaperone Plasmid conjugation A B ST R AC T Antisense RNAs have long been known to regulate diverse aspects of plasmid biology. Here we review the FinOP system that modulates F plasmid gene expression through regula- tion of the F plasmid transcription factor, TraJ. FinOP is a two component system composed of an antisense RNA, FinP, which represses TraJ translation, and a protein, FinO, which is required to stabilize FinP and facilitate its interactions with its traJ mRNA target. We review the evidence that FinO acts as an RNA chaperone to bind and destabilize internal stem- loop structures within the individual RNAs that would otherwise block intermolecular RNA duplexing. Recent structural studies have provided mechanistic insights into how FinO may facilitate interactions between FinP and traJ mRNA. We also review recent findings that two other proteins, Escherichia coli ProQ and Neisseria meningitidis NMB1681, may repre- sent FinO-like RNA chaperones. © 2014 Elsevier Inc. All rights reserved. 1. Introduction The importance of small, non-coding RNAs (ncRNAs) 1 that regulate gene expression in all kingdoms of life is becoming increasingly clear. ncRNA function involves base pairing with either RNA or DNA targets in an energetically favorable interaction that in theory should require no enzyme co-factors. However, the interaction of two nucleic acid polymers often involves the destabilization of inter- nal structures (e.g., hairpins) within the individual nucleic acids. Although these internal structures are less energet- ically favorable than the final paired structure (e.g., duplex) between the two molecules, the bimolecular interaction may be kinetically unlikely in the absence of factors that can destabilize the internal structures as a first step in the process. This paradox lead to the proposal of the RNA chaperone hypothesis by Herschlag (1995) and it is now widely believed that RNA-based regulatory processes often require protein co-factors that may act as chaperones to regulate RNA-target interactions. In bacteria, the best characterized RNA chaperone is the Sm protein Hfq, which forms hexameric ring structures that provide multiple binding surfaces for RNAs (for recent reviews, see (Weichenrieder, 2014; Sauer, 2013; Wagner, 2013; Wilusz and Wilusz, 2013). Here we review the evidence that the regulatory protein FinO of F-like plasmids represents another class of bacterial RNA chaperones. Whereas FinO is best characterized as a critical inhibitor of the F plasmid tra operon, recent findings indicate that FinO-like proteins with RNA chaperone activity may be widespread throughout bacterial species. 2. Discovery of an antisense RNA system that regulates F plasmid gene expression Antisense RNA, defined as a transcript that is expressed in cis to its target RNA, has a long and important associa- tion with plasmid biology. It has been the subject of intense study on the regulation of replication initiation and copy number control, expression of antidotes to post-segregational * Corresponding author. E-mail address: mark.glover@ualberta.ca (J.N. Mark Glover). 1 Abbreviations: ncRNA, non-coding RNA; HF, Thigh frequencies of transfer; UTR, untranslated region; FRET, Förster resonance energy trans- fer; SAXS, small angle X-ray scattering. http://dx.doi.org/10.1016/j.plasmid.2014.07.003 0147-619X/© 2014 Elsevier Inc. All rights reserved. Plasmid 78 (2015) 79–87 Contents lists available at ScienceDirect Plasmid journal homepage: www.elsevier.com/locate/yplas