Structure, function and RNA binding mechanisms of the prokaryotic Sm-like protein Hfq

Over the last decade it has become increasingly clear that the Sm-like (Lsm) protein Hfq, initially identified as a host factor required for Qß bacteriophage replication, acts as a global post-transcriptional regulator in enterobacteria (reviewed in Valentin-Hansen et al. 2004; Storz et al. 2004; Gottesman et al. 2006; Vogel 2009a). Most of our current knowledge derives from detailed studies of small regulatory RNAs (sRNAs) in Escherichia coli and Salmonella. In particular, Hfq has been implicated in the regulation of translation and stability of an increasing number of mRNAs and its action has been shown to be intimately linked with the activity of a family of chromosomally encoded sRNAs that function in post-transcriptional control by base-pairing with cognate target mRNAs. Hfq associates with both regulatory RNAs and target RNA(s) and is required for proper riboregulation in enterobacteria. The importance of Hfq is further underscored by its multiple roles in bacterial physiology, including stress responses, bacteriocin production, nitrogen fixation, symbiosis, motility, quorum sensing and virulence of various bacterial pathogens (for reviews of Hfq activities see Vassilieva and Garber 2002; Valentin-Hansen et al. 2004; Dienst et al. 2008; Fröhlich and Vogel 2009). Here I will focus on novel findings about Hfq, its structure, RNA-binding mechanisms and mode of action in riboregulation and mRNA decay.