Sequence and expression of four mutant asparic acid tRNA genes from the mitochondria ofSaccharomyces cerevisiae

Abstract

Expression of the mitochondrial tRNA ^Asp gene of Saccharomyces cerevisiae has been examined in five syn₋ mutants known to affect tRNA ^Asp function, and in a rho⁻ mutant which accumulates precursor tRNAs. By comparison of wild-type versus mutant DNA sequence, the lesion in each syn⁻ mutant has been identified as a single base change within the mitochondrial tRNA^Asp structural gene. The mutant tRNA ^Asp genes are transcribed, and the transcripts can be processed to mature 45-size tRNA ^Asp. The steady-state level of each mutant tRNA ^Asp is lower than that of wild-type tRNA ^Asp. The RNA from two of the syn⁻ mutants contained a second, slow-migrating from of mitochondrial tRNA ^Asp which is correctly processes at the 5' end. We conclude that the lesions in the syn⁻ mitochondrial tRNA genes block neither transcription of these genes, nor 5' end processing of the transcripts. The effects of each point mutation must be manifested at the level of 3' end processing, or at a functional level.