PROPERTIES OF TWO NUCLEASE GENES IN NEUROSPORA CRASSA

Kohji Hasunuma ¹ and Tatsuo Ishikawa ²

¹ Department of Botany, Faculty of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
² Institute of Applied Microbiology, University of Tokyo, Bunkyo-ku, Tokyo, Japan

Two genes, nuc-1 and nuc-2, of Neurospora crassa which were responsible for the nucleic acid digestion, were located on linkage group 1 and 2, respectively. A temperature-sensitive mutant (B1ts-2) was obtained from a nuc-2 mutant. Nuclease mutants showed a reduced activity of nuclease N₃ which was found to be a complex consisting of nuclease N₃^' and inhibitor molecule. Nuclease N₃, nuclease N₃^' and inhibitor were partially purified and estimated to have the approximate molecular weights of 38,000, 12,500 and 25,000 respectively. A nuc-1 mutant produced the nuclease N₃^' altered in thermolability. A nuc-2 mutant and B1ts-2 produced the inhibitor altered in the capacity to inhibit nuclease N₃^' activity. The inhibitor prepared from B1ts-2 was more thermostable than that from other strains. From these results, it was suggested that the nuc-1 gene is the structural gene for nuclease N₃^' and the nuc-2 gene that for the inhibitor. A possible involvement of this enzyme-inhibitor complex in the regulation of nuclease activity and synthesis of other proteins was suggested.