Thesis

A comparison of phosphoserine phosphatase in two allelic serine requiring mutants of Neurospora crassa

The phosphorylated pathway has been proposed as the major source of serine in Neurospora Crassa (Sojka & Garner, 1967). Chuck (1980) demonstrated that a serine deficient mutant of Neurospora crassa, ser (JBM5), which is isogenic with its progenitor prototrophic strain, shows a marked decrease in its phosphoserine phosphatase specific activity when compared to the activity of its prototrophic strain. This lowered activity in the enzyme catalyzing the terminal step of the phosphorylated pathway of serine biosynthesis in a serine requiring mutant which has a single gene difference compared to its prototrophic strain supported the phosphorylated pathway as the major source of serine in Neurospora crassa. The present study assayed the phosphoserine phosphatase activities of two allelic serine requiring mutants of Neurospora crassa, ser-3 and ser (JBM5). In all assays, both mutants had significantly lower phosphoserine phosphatase specific activities than did their respective prototrophic strains. This finding lends further support to the phosphorylated pathway as the principal route of serine biosynthesis in Neurospora crassa.

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