title: Conserved but nonessential interaction of SRP RNA with translation factor EF-G.
abstract: 4.5S RNA is essential for viability of Escherichia coli, and forms a key component of the signal recognition particle (SRP), a ubiquitous ribonucleoprotein complex responsible for cotranslational targeting of secretory proteins. 4.5S RNA also binds independently to elongation factor G (EF-G), a five-domain GTPase that catalyzes the translocation step during protein biosynthesis on the ribosome. Point mutations in EF-G suppress deleterious effects of 4.5S RNA depletion, as do mutations in the EF-G binding site within ribosomal RNA, suggesting that 4.5S RNA might play a critical role in ribosome function in addition to its role in SRP. Here we show that 4.5S RNA and EF-G form a phylogenetically conserved, low-affinity but highly specific complex involving sequence elements required for 4.5S binding to its cognate SRP protein, Ffh. Mutational analysis indicates that the same molecular structure of 4.5S RNA is recognized in each case. Surprisingly, however, the suppressor mutant forms of EF-G bind very weakly or undetectably to 4.5S RNA, implying that cells can survive 4.5S RNA depletion by decreasing the affinity between 4.5S RNA and the translational machinery. These data suggest that SRP function is the essential role of 4.5S RNA in bacteria.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA.
authors.forename: Madi Bidya
authors.initials: MB
authors.lastname: Sagar
authors.forename: Louise
authors.initials: L
authors.lastname: Lucast
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Doudna
mesh_terms: D001483:Base Sequence; D017124:Conserved Sequence; D008969:Molecular Sequence Data; D009154:Mutation; D020653:Peptide Elongation Factor G / Q000235:genetics / Q000378:metabolism*; D012313:RNA / Q000378:metabolism*; D012329:RNA, Bacterial; D012335:RNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D018271:Signal Recognition Particle / Q000235:genetics* / Q000378:metabolism
chemical_list: C409968:4.5S RNA; D020653:Peptide Elongation Factor G; D012329:RNA, Bacterial; D012335:RNA, Ribosomal; D018271:Signal Recognition Particle; D012313:RNA