Functional replacement of the Escherichia coli hfq gene by the homologue of Pseudomonas aeruginosa

The 102 aa Hfq protein of Escherichia coli (Hfq(Ec)) was first described as a host factor required for phage Qbeta replication. More recently, Hfq was shown to affect the stability of several E. coli mRNAs, including ompA mRNA, where it interferes with ribosome binding, which in turn results in rapid degradation of the transcript. In contrast, Hfq is also required for efficient translation of the E. coli and Salmonella typhimurium rpoS gene, encoding the stationary sigma factor. In this study, the authors have isolated and characterized the Hfq homologue of Pseudomonas aeruginosa (Hfq(Pa)), which consists of only 82 aa. The 68 N-terminal amino acids of Hfq(Pa) show 92 % identity with Hfq(Ec). Hfq(Pa) was shown to functionally replace Hfq(Ec) in terms of its requirement for phage Qbeta replication and for rpoS expression. In addition, Hfq(Pa) exerted the same negative effect on E. coli ompA mRNA expression. As judged by proteome analysis, the expression of either the plasmid-borne hfq(Pa) or the hfq(Ec) gene in an E. coli Hfq(-) RpoS(-) strain revealed no gross difference in the protein profile. Both Hfq(Ec) and Hfq(Pa) affected the synthesis of approximately 26 RpoS-independent E. coli gene products. These studies showed that the functional domain of Hfq resides within its N-terminal domain. The observation that a C-terminally truncated Hfq(Ec) lacking the last 27 aa [Hfq(Ec(75))] can also functionally replace the full-length E. coli protein lends further support to this notion.