Sequence analysis of the pyr-4 (orotidine 5'-P decarboxylase) gene of Neurospora crassa.

The pyr-4 gene of Neurospora crassa encodes orotidine-5' -phosphate decarboxylase, which catalyses the sixth step in the pyrimidine biosynthetic pathway. The complete nucleotide sequence of a 1.8-kb genomic fragment containing the pyr-4 gene has been determined. Using transposon mutagenesis, the coding region has been identified, and the amino acid (aa) sequence deduced. Comparison of the pyr-4 aa sequence with URA3, the equivalent gene of Saccharomyces cerevisiae, showed extensive blocks of homology, with non-homologous sequences between these blocks being generally much longer in Neurospora than in yeast. Computer-predicted protein secondary structure of pyr-4 and URA3 was conserved within equivalent blocks. Upstream sequences of pyr-4 were compared with other sequenced Neurospora genes and possible promoter sequences identified.