ISOLATION AND ANALYSIS OF THE ARG-13 GENE OF NEUROSPORA-CRASSA

Mutations in arg-13 result in slow growth in minimal medium and can su ppress mutations in carbamyl phosphate synthase-aspartate carbamyl tra nsferase within the pyrimidine pathway; the exact biochemical function of the gene product is unknown. To understand the role of arg-13 in a rginine metabolism, cosmids rescuing growth in arg-13 mutants were clo ned and mapped to the position of arg-13 on LG IR. Northern analysis s howed the arg-13 message to contain similar to 2100 nt, although a 1.4 -kb genomic fragment truncated at the 5' and 3' ends of the gene encod es a shortened transcript that can rescue arg-13 function. Expression of mRNA arising from the mutant arg-13 gene is induced by arginine sta rvation, although wild type (arg-13(+)) is not derepressed in minimal medium. The sequence of the arg-13 gene shows ARG-13 to be a member of the mitochondrial carrier superfamily with three repeats of a similar to 100-amino acid domain, six putative membrane spanning regions, and three copies of the mitochondrial carrier consensus pattern. This inf ormation plus available and new nutritional data are consistent with t he hypothesis that arg-13 encodes a mitochondrial basic amino acid car rier whose existence was predicted based upon previous physiological, nutritional and biochemical data.