Cloning, sequencing, and characterizing the Lactobacillus leichmannii pyrC gene encoding dihydroorotase.

The gene encoding dihydroorotase (DHOase) of Lactobacillus leichmannii, the third enzyme of the pyrimidine biosynthetic pathway (Genbank (EMBL) accession no X78999), was cloned by phenotypic complementation of an E coli pyrC deficient mutant after transformation with Lactobacillus leichmannii genomic library DNA. The open reading frame of the L leichmannii pyrC gene spans 1281 bp and codes for a 427 amino cid polypeptide with a calculated M(r) of 46,316 Da. Primer extension showed that the initiation site for transcription is 37 bp upstream of the putative start codon ATG and Northern blot analysis confirmed its independent transcription from the adjacent pyrB gene. Comparison of the deduced amino acid sequence of L leichmannii DHOase with sequences established for other organisms yielded 46.6% identity with the corresponding Bacillus subtilis enzyme. Highly conserved protein domains suggest importance for the enzyme's function.