Nucleic Acids Research, 1988, Vol. 16, No. 19 9081-9095
© 1988
Articles |
A mitochondrial intergenic mutation affecting processing of specific yeast mitochondrial transcripts
Department of Biochemistry and Centre for Molecular Biology and Medicine, Monash University Clayton, Victoria 3168, Australia
*To whom correspondence should be addressed
Received August 4, 1988. Accepted September 5, 1988.
The mutation in the temperature-conditional mit- mutant h56, mapped previously to the varl gene region of Saccharomyces cerevisiae mitochondrial DNA, results in a specific inhibition of varl protein synthesis in cells incubated at the non-permissive temperature, 36°C (1). We have now characterized the mutation present in mutant h56 by DNA sequencing and found it to be an A to T transversion located 109 nucleotides upstream of the varl reading frame. Two spontaneous revertants of mutant h56 restore the parental strain sequence at residue -109, confirming that this single base change within the 5'-untranslated region of the varl mRNA is responsible for defective synthesis of the varl protein. A comparison of varl transcripts in the parental and mutant strains has shown that the mutation specifically blocks formation of varl mRNA at 36°C and leads to accumulation of precursor transcripts. Expression of the olil gene, co-transcribed with the varl gene in primary transcripts, is not affected. It is concluded that the mutation in mutant h56 alters the secondary structure of the precursor RNA, inhibiting an endonucleolytic cleavage required to generate the 5' end of varl mRNA.