Expression of the γ‐subunit gene of desulfoviridin‐type dissimilatory sulfite reductase and of the α‐ and β‐subunit genes is not coordinately regulated

Abstract

It has been shown [Pierik, A. J., Duyvis, M. G., van Helvoort, J. M. L. M., Wolbert, R. B. G. & Hagen, W. R. (1992) Eur. J. Biochem. 205, 111–115] that desulfoviridin, the dissimilatory sulfite reductase of sulfate‐reducing bacteria of the genus Desulfovibrio, contains a third, γ, subunit (11 kDa), in addition to the well‐established α (50 kDa) and β (40 kDa) subunits, and an α₂β₂γ₂ subunit structure has been proposed. Cloning and sequencing of the dsvC gene indicated it to encode a protein of 105 amino acids (11.9 kDa; γ subunit). The finding that the dsvC gene, located on a 3.5‐kb SacII fragment, is transcribed in both Escherichia coli and Desulfovibrio vulgaris as an mRNA of only 400–600 nucleotides, and that both the dsvA and dsvB genes are present on a 7.2‐kb SacII fragment, indicates that dsvC forms a separate transcriptional unit. The steady‐state level of α and β subunits expressed in D. vulgaris Hildenborough cells is rather constant, while that of the γ subunit increased strongly in the stationary growth phase. Biochemical analysis of the purified protein, expressed in E. coli, and library comparison of its sequence, have so far failed to establish the function of γ.