Molecular cloning of thi-4, a gene necessary for the biosynthesis of thiamine in Neurospora crassa

The thiamine-4 (thi-4) gene was cloned by functional complementation of a thi-4 mutant of Neurospora crassa. The product of this gene is believed to be involved in the condensation of pyrimidine and thiazole precursors, which is necessary for the synthesis of thiamine. The thi-4 gene has ten introns which vary in length from 57 to 200 bp and the junction and internal (lariat) sequences are in good agreement with the consensus sequences for the splicing of introns in N. crassa. The thi-4 gene encodes a protein of 538 amino acids which is similar in terms of amino-acid sequence to proteins encoded by Saccharomyces cerevisiae whose function is unknown. The expression of the thi-4 gene in N. crassa was not repressed by thiamine.