Novel Mutation Causing Derepression of Several Enzymes of Sulfur Metabolism in Neurospora crassa

Abstract

A group of enzymes of sulfur metabolism (arylsulfatase, cholinesulfatase, and a number of others) are normally repressed in Neurospora crassa by an abundant supply of a “favored” sulfur source such as methionine or inorganic sulfate. A mutant called scon c was isolated in which the formation of each of these enzymes is largely or completely nonrepressible. The structural genes for three of these enzymes have been mapped; scon c is not linked to any of them. It is also not linked to cys-3 , another gene which is involved in control of the same group of enzymes. Two alleles of the structural gene for arylsulfatase [ ars + and ars ( UFC-220 )] produce electrophoretically distinguishable forms of arylsulfatase. Heterokaryons with the constitution scon c ars + + scon + ars ( UFC-220 ) were prepared. These heterokaryons produce both forms of arylsulfatase under conditions of sulfur limitation, but produce only the wild-type ( ars + ) form under conditions of sulfur abundance. When the alleles of ars and scon are in the opposite relationship, only the ars ( UFC-220 ) form of arylsulfatase can be detected under conditions of sulfur abundance. Thus the effect of the scon c mutation seems to be limited to its own nucleus. The implications of these findings are discussed.