The widely conserved Era G-protein contains an RNA-binding domain requiredfor Era function in vivo

Era is a small G-protein widely conserved in eubacteria and eukaryotes. Alt hough essential for bacterial growth and implicated in diverse cellular pro cesses, its actual function remains unclear. Several lines of evidence sugg est that Era may be involved in some aspect of RNA biology. The GTPase doma in contains features in common with all G-proteins and is required for Era function in vivo. The C-terminal domain (Era(CTD)) bears scant similarity t o proteins outside the Era subfamily. On the basis of sequence comparisons, we argue that the Era(CTD) is similar to, but distinct from, the KH RNA-bi nding domain. Although both contain the consensus VIGxxGxxl RNA-binding mot if, the protein folds are probably different. We show that bacterial Era bi nds RNA in vitro and can form higher-order RNA-protein complexes. Mutations in the VIGxxGxxl motif and other conserved residues of the Escherichia coi l Era(CTD) decrease RNA binding in vitro and have corresponding effects on Era function in vivo, including previously described effects on cell divisi on and chromosome partitioning. Importantly, mutations in L-66, located in the predicted switch II region of the E. coil Era GTPase domain, also pertu rb binding, leading us to propose that the GTPase domain regulates RNA bind ing in response to unknown cellular cues. The possible biological significa nce of Era RNA binding is discussed.