Mutant Tyrosine Transfer Ribonucleic Acids

Three independent mutants of the suIII tyrosine suppressor transfer RNA gene have been isolated. These mutants are shown to produce mutant tRNA's differing from the wild-type suIII+ tRNA molecule in each case by a single base change. A mutant tRNA containing an A residue in place of a G in the “dihydrouracil loop” appears to be defective in a step in protein synthesis occurring after the acylated tRNA is bound to the ribosome. A mutant tRNA having an A residue in place of a G in the “anticodon stem” appears to be defective exclusively in its apparent affinity for the tyrosyl tRNA synthetase. The isolation of mutant tRNA's as well as their biological properties are discussed.