BIOSYNTHESIS OF RIBOFLAVIN - CHARACTERIZATION OF THE BIFUNCTIONAL DEAMINASE-REDUCTASE OF ESCHERICHIA-COLI AND BACILLUS-SUBTILIS

The ribG gene at the 5' end of the riboflavin operon of Bacillus subti lis and a reading frame at 442 kb on the Escherichia coli chromosome ( subsequently designated ribD) show similarity with deoxycytidylate dea minase and,vith the RIB7 gene of Saccharomyces cerevisiae, The ribG ge ne of B. subtilis and the ribD gene of E. coli were expressed in recom binant E. coli strains and were shown to code for bifunctional protein s catalyzing the second and third steps in the biosynthesis of ribofla vin, i.e., the deamination of 2,5-diamino-6 ribosylamino-4(3H)-pyrimid inone 5'-phosphate (deaminase) and the subsequent reduction of the rib osyl side chain (reductase), The recombinant proteins specified by the ribD gene of E. coli and the ribG gene of B. subtilis were purified t o homogeneity, NADH as well as NADPH can be used as a cosubstrate for the reductase of both microorganisms under study, Expression of the N- terminal or C-terminal part of the RibG protein yielded proteins with deaminase or reductase activity, respectively; however, the truncated proteins were rather unstable.