Isolation and analysis of the arg-13 gene of Neurospora crassa

Mutations in arg-13 result in slow growth in minimal medium and can suppress mutations in carbamyl phosphate synthase-aspartate carbamyl transferase within the pyrimidine pathway; the exact biochemical function of the gene product is unknown. To understand the role of arg-13 in arginine metabolism, cosmids rescuing growth in arg-13 mutants were cloned and mapped to the position of arg-13 on LG IR. Northern analysis showed the arg-13 message to contain approximately 2100 nt, although a 1.4-kb genomic fragment truncated at the 5' and 3' ends of the gene encodes a shortened transcript that can rescue arg-13 function. Expression of mRNA arising from the mutant arg-13 gene is induced by arginine starvation, 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 approximately 100-amino acid domain, six putative membrane spanning regions, and three copies of the mitochondrial carrier consensus pattern. This information plus available and new nutritional data are consistent with the hypothesis that arg-13 encodes a mitochondrial basic amino acid carrier whose existence was predicted based upon previous physiological, nutritional and biochemical data.