Modifying Factors of Amino-acid Antagonisms in a Mutant of Neurospora crassa

Abstract

IN certain amino-acid-requiring mutants of Neurospora crassa, any one of a number of naturally occurring amino-acids can inhibit competitively the utilization of the required amino-acid for growth^1,2. In the course of determining the inhibition indexes of the inhibitory amino-acids, it was noted that variations in certain experimental conditions would cause significant differences in the observed indexes. The mutant strain E-5212 (ref. 3), which responds to either phenylalanine or phenylpyruvate, was used in a study of the various modifying factors. Growth assays were performed in the usual manner using Fries minimal medium⁴. The inhibition index is defined as the ratio of inhibitor to required amino-acid which produces complete inhibition of growth for approximately three days at 27° C.