The research proposed is directed at obtaining a better understanding of the genetics and biochemistry of the ribosomes of an eukaryote, Saccharomyces cerevisiae. This goal will be approached (1) by the isolation and characterization of antibiotic resistant and temperature-sensitive mutants that result in alterations in ribosomal proteins, (2) by a study of the newly discovered phenomenon of phenotypic suppression in yeast, for example, the identification of ram-type mutants, (3) by the attempted identification of ribosomal protein genes by analysis of hybrid Saccharomyces species and by the formation of recombinant hybrids between yeast ribosomal genes and bacteriophage lambda, and (4) by studies of the mode of action of antibiotics that inhibit translation in eukaryotes such as yeast. In addition, as a separate project, we plan to continue with our analysis of ribosome mutants in E. coli that are resistant to novel antibiotics not previously studied in this organism. We expect to obtain new classes of ribosome mutants to aid in structure-function studies of bacterial ribosomes.