Properties of a protein antigenically related to tryptophan synthetase in Neurospora crassa.

Sufficient evidence has accumulated in recent years, in part through gene enzyme studies in microorganisms (Bonner, 1951; Yanofsky, 1956), to implicate the gene as a regulator of certain qualitative and quantitative aspects of protein formation (Horowitz, 1956). Although examples of alterations in protein structure arising through gene mutation are limited in number, there are many cases in which gene change has resulted in the loss of a specific enzymatic activity. Since the basis for detecting an enzyme deficiency primarily rests on an inability to demonstrate enzymatic activity under various experimental conditions (Mitchell and Lein, 1948; Yanofsky, 1952) several fundamental problems arise. It is of the greatest interest to know whether enzyme deficiencies represent a complete loss of the capacity to synthesize the enzyme, or whether molecules structurally similar to the enzyme, but devoid of enzymatic activity, continue to be formed. This aspect of the problem becomes particularly significant in those cases where numerous mutations at a particular locus have been observed to cause the same enzyme deficiency (Yanofsky and Bonner, 1955a, 1955b). One wonders whether in such instances each of the mutations has actually affected the synthesis of the protein in exactly the same manner, or whether such enzyme deficiencies really reflect a damage to different sensitive areas within the gene, each of which is essential for the formation of the fully active enzyme molecule (Yanofsky, 1956; Suskind, 1956a; Bonner, 1956). Answers to some of these questions have recently been sought by employing immunochemical methods to study certain allelic tryptophan requiring mutants (td) of Neurospora crassa unable to form the enzyme tryptophan synthetase (Suskind et al., 1955). Evidence has been obtained