A Gene Modifying the Thiamine-requirement of Strains of Neurospora crassa

Abstract

A new gene, thi-lo, is described in Neurospora crassa. This gene is shown to be a modifier of the nutritional response of strains containing the thi-1 gene, and is not nutritionally detectable in the absence of the thi-1 mutant locus. The gene thi-lo is additionally characterized by a decreased ability to synthesize thiamine from thiazole and pyrimidine; thi-lo appears to modify only thi-1 strains because of their unusually high thiamine requirements. The nutritional responses of strains containing either thi-2 or thi-3 loci are not affected by the presence of thi-lo. Both thi-lo and thi-4 are anomalous in the condensation of pyrimidine and thiazole. The probability that thi-lo may be an isoallele of thi-4 is based upon a similarity of metabolic pattern and upon location on chromosome III. The failure to obtain recombination in crosses between strains containing thi-lo and thi-4 constitutes additional support for their allelism.