STRUCTURAL-ANALYSIS OF THE FDS OPERON ENCODING THE NAD(-LINKED FORMATE DEHYDROGENASE OF RALSTONIA-EUTROPHA())

The fdsGBACD operon encoding the four subunits of the NAD(+)-reducing formate dehydrogenase of Ralstonia eutropha H16 was cloned and sequenc ed. Sequence comparisons indicated a high resemblance of FdsA (alpha-s ubunit) to the catalytic subunits of formate dehydrogenases containing a molybdenum (or tungsten) cofactor. The NH2-terminal region (residue s 1-240) of FdsA, lacking in formate dehydrogenases not linked to NAD( P)(+), exhibited considerable similarity to that of NuoG of the NADH:u biquinone oxidoreductase from Escherichia coli as well as to HoxU and the NH2-terminal segment of HndD of NAD(P)(+)-reducing hydrogenases. F dsB (beta-subunit) and FdsG (gamma-subunit) are closely related to Nuo F and NuoE, respectively, as well as to HoxF and HndA. It is proposed that the NH2-terminal domain of FdsA together with FdsB and FdsG const itute a functional entity corresponding to the NADH dehydrogenase (dia phorase) part of NADH:ubiquinone oxidoreductase and the hydrogenases. No significant similarity to any known protein was observed for FdsD ( delta-subunit). The predicted product of fdsC showed the highest resem blance to FdhD from E. coli, a protein required for the formation of a ctive formate dehydrogenases in this organism. Transcription of the fd s operon is subject to formate induction. A promoter structure resembl ing the consensus sequence of sigma(70)-dependent promoters from E. co li was identified upstream of the transcriptional start site determine d by primer extension analysis.