The Ustilago maydis pyr3 gene: sequence and transcriptional analysis.

The pyr3 gene of Ustilago maydis encodes a 391-amino acid (aa) polypeptide. The sequence has identifies with dihydro-orotases (DHOases) from other organisms, but is most related to sequences of other monofunctional enzymes. The polypeptide contains the three domains conserved in other DHOases. The polypeptide encoded by the pyr3-1 allele has an aa change seven residues away from the C-terminal conserved domain. Transcription start point (tsp) is 58 nucleotides upstream from the start codon, and is in a region characterised by CTTT and CATC motifs. In the absence of TATA and CAAT boxes, these motifs might be important in transcriptional regulation. Gene disruption experiments suggest that the pyr3 gene product might have another function in addition to that in pyrimidine biosynthesis.