This proposal concerns the isolation and mapping of mutant tRNA genes, in yeast, which are recognized as informational suppressors. New phenotypic classes of nonsense suppressors and missense suppressors will be sought to broaden the variety of tRNA genes that are genetically marked. The suppressor genes are useful probes for both physiological and molecular biological approaches to the study of protein synthesis. An ancillary project concerns the genetics of an interspecific hybrid in yeast. In particular, the factors involved in the pairing of homoeologous chromosomes will be studied. This particular hybrid reveals polymorphisms of the DNA which can be exploited for the cloning of suppressor tRNA genes by molecular biologists.