Multiple functions of an evolutionarily conserved RNA binding domain.

Ribosomal protein L30 of Saccharomyces cerevisiae binds to a distinct RNA structure to inhibit the splicing and the translation of its own transcript. Remarkably, the ortholog of L30 from the archaeon Sulfolobus acidocaldarius binds specifically to the same RNA fragment and inhibits splicing both in vitro and in vivo. Indeed, expression of Sulfolobus L30 in yeast severely reduces growth by limiting production of the endogenous L30. This conservation of binding specificity implies that the target of regulation in the RPL30 transcript mimics a site in the rRNA that has been conserved for more than a billion years. We identify this site, whose location suggests that L30, which has no apparent eubacterial ortholog, is responsible for establishing the orientation of a key bridge between the large and small ribosomal subunits.