Enzymatic activity of a genetically altered tryptophan synthetase in Neurospora crassa. 
Partially purified preparations of certain tryptophan-requiring mutants of Neurospora crassa, which contain a protein (CRM) antigenically related to wild-type tryptophan synthetase, possess indole glycerol phosphate-synthesizing activity.  This activity can be inhibited by anti-CRM sera.  It is suggested that CRM in such mutants represents a damaged tryptophan synthetase lacking the capacity to react with l-serine.