THE STRUCTURE OF RIBOSOMAL PROTEIN-S5 REVEALS SITES OF INTERACTION WITH 16S RIBOSOMAL-RNA

UNDERSTANDING the process whereby the ribosome translates the genetic code into protein molecules will ultimately require high-resolution structural information, and we report here the first crystal structure of a protein from the small ribosomal subunit. This protein, S5, has a molecular mass of 17,500 and is highly conserved in all lifeforms1-4. The molecule contains two distinct alpha/beta-domains that have structural similarities to several other proteins that are components of ribonucleoprotein complexes. Mutations in S5 result in several phenotypes which suggest that S5 may have a role in translational fidelity and translocation. These include ribosome ambiguity or ram5, reversion from streptomycin dependence6 and resistance to spectinomycin6. Also, a cold-sensitive, spectinomycin-resistant mutant of S5 has been identified which is defective in initiation7. Here we show that these mutations map to two distinct regions of the molecule which seem to be sites of interaction with ribosomal RNA. A structure/function analysis of the molecule reveals discrepancies with current models8,9 of the 30S subunit.