Ribonucleotide reductase (RNR) of Corynebacterium glutamicum ATCC 13032--genetic characterization of a second class IV enzyme.

Ribonucleotide reductases (RNRs) encoded by nrd (nucleotide reduction) genes are unique enzymes providing the DNA precursors in all living organisms and several viruses. The designation of four classes of RNRs reflects their use of diverse metallo-cofactors. Using oligonucleotide primers derived from conserved domains of the primary structure of known NrdA and NrdE proteins, an internal 938 bp fragment of the nrdE gene was amplified from genomic DNA of Corynebacterium glutamicum. With this PCR product a 4.36 kb fragment was identified and cloned containing the nrdHIE genes of C. glutamicum. A probe derived from nrdF2 of Mycobacterium tuberculosis allowed the cloning and sequencing of the nrdF gene located 3.1 kb further downstream, encoding the small subunit of the C. glutamicum RNR. Conjugative introduction of nrdE from C. glutamicum complemented thermosensitive mutants of Corynebacterium ammoniagenes which had a defective catalytic subunit of the Mn-RNR. The authors provide arguments for allocation of the C. glutamicum NrdEF proteins to class IV in the RNR classification scheme of Stubbe & van der Donk (1995) [Chem Biol 2, 793-801].