Studying the Properties of Domain I of the Ribosomal Protein L1: Incorporation into Ribosome and Regulation of the L1 Operon Expression

L1 is a conserved protein of the large ribosomal subunit. This protein binds strongly to the specific region of the high molecular weight rRNA of the large ribosomal subunit, thus forming a conserved flexible structural element—the L1 stalk. L1 protein also regulates translation of the operon that comprises its own gene. Crystallographic data suggest that L1 interacts with RNA mainly by means of its domain I. We show here for the first time that the isolated domain I of the bacterial protein L1 of Thermus thermophilus and Escherichia coli is able to incorporate in vivo into the E. coli ribosome. Furthermore, domain I of T. thermophilus L1 can regulate expression of the L1 gene operon of Archaea in the coupled transcription–translation system in vitro, as well as the intact protein. We have identified the structural elements of domain I of the L1 protein that may be responsible for its regulatory properties.