1. Acetylglutamate kinase-acetylglutamyl-phosphate reductase complex of Neurospora crassa. Evidence for two polypeptides.
- Author
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Wandinger-Ness, AU, Wolf, EC, Weiss, RL, and Davis, RH
- Subjects
Biochemistry and Cell Biology ,Biological Sciences ,Genetics ,Aldehyde Oxidoreductases ,Genes ,Fungal ,Models ,Genetic ,Molecular Weight ,Mutation ,Neurospora ,Neurospora crassa ,Phosphotransferases ,Phosphotransferases (Carboxyl Group Acceptor) ,RNA ,Fungal ,RNA ,Messenger ,Chemical Sciences ,Medical and Health Sciences ,Biochemistry & Molecular Biology ,Biological sciences ,Biomedical and clinical sciences ,Chemical sciences - Abstract
Mutations at the arg-6 locus in Neurospora crassa are divided into two complementation groups (A and B) and a third noncomplementing group. There are many suppressible nonsense mutations among mutants in complementation group B and one in the noncomplementing group; no nonsense mutations exist among mutants in complementation group A (Davis, R. H., and Weiss, R. L. (1983) Mol. Gen. Genet. 192, 46-50). We show here that the mutants are defective in either or both of two enzymes of arginine biosynthesis, acetylglutamate kinase and/or acetylglutamyl-phosphate reductase. Mutants in complementation group A lack acetylglutamate kinase, those in complementation group B lack acetylglutamyl-phosphate reductase, and those in the noncomplementing group lack both activities. Mutants in group B also have reduced levels of acetylglutamate kinase. The enzymes from purified mitochondria are readily separable by gel filtration and by Blue A dye affinity chromatography. Acetylglutamate kinase appears to be an octamer with a molecular weight of 400,000, whereas acetylglutamyl-phosphate reductase appears to be a dimer with a molecular weight of 93,000. This suggests that the two activities reside on distinct polypeptides. These results are best accommodated by the following model: the arg-6 locus encodes a single mRNA which is translated into a single polypeptide; the latter is then cleaved post-translationally to yield two physically separable enzymes.
- Published
- 1985