IDENTIFICATION AND CLONING OF THE MYCOBACTERIUM-AVIUM FOLA GENE, REQUIRED FOR DIHYDROFOLATE-REDUCTASE ACTIVITY

Dihydrofolate reductase is an essential bacterial enzyme necessary for the maintenance of intracellular folate pools in a biochemically acti ve reduced state. In this report, the Mycobacterium avium folA gene wa s identified by functional genetic complementation, sequenced, and exp ressed for the first time. It has an open reading frame of 543 bp with a G+C content of 73%. The translated polypeptide sequence shows 58% i dentity to the consensus sequence of the conserved regions from eight other bacterial dihydrofolate reductases. Recombinant M. avium dihydro folate reductase was expressed actively in Escherichia coli, and SDS-P AGE analysis revealed a 20 kDa species, agreeable with that predicted from the polypeptide sequence.