The pyrAb gene coding for the large subunit of carbamoylphosphate synthetase from Bacillus stearothermophilus: molecular cloning and functional characterization.

The Bacillus stearothermophilus pyrAb gene, encoding the large subunit of carbamoylphosphate synthetase, was isolated and characterized. The DNA sequence is a 3195-nucleotide long reading frame coding for a polypeptide of 1064 amino acids and deduced Mr approximately 116,160 Da. The pyrAb gene is part of the B. stearothermophilus pyrimidine biosynthesis operon pyr. The 5' end of thepyrAb gene overlaps with the 3' end of the pyrAa gene coding for the small subunit of carbamoylphosphate synthetase, while the 3' end of the pyrAb gene is overlapped with the 5' end of the pyrD gene, which by analogy with the B. subtilis genomic organization, codes for dihydroorotate dehydrogenase. The deduced amino acid sequence of the large subunit of B. stearothermophilus carbamoylphosphate synthetase was compared with the known sequences of the large subunit of carbamoylphosphate synthetase enzymes from other organisms via the NCBI database. Extremely high (98%) identity in amino acid sequence with the large subunit of carbamoylphosphate synthetase from Bacillus caldolyticus was detected.