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

51 that desulfoviridin, the dissimilatory sulfite reductase of sulfate-reducing bacteria of the genus Desulfovibrio, contains a third, y, subunit (1 1 kDa), in addition to the well-established a (50 kDa) and p (40 kDa) subunits, and an a 2 j z y z subunit structure has been proposed. Cloning and sequencing of the dsvC gene indicated it to encode a protein of 105 amino acids (1 1.9 kDa; y subunit). The finding that the dsvC gene, located on a 3.5-kb SacII fragment, is transcribed in both Escherichia coli and Desulfovihrio vulgaris as an mRNA of only 400-600 nucleotides, and that both the dsvA and dsvB genes are present on a 7. (66 kDa) subunits of the a&, assimilatory sulfite reductase from Salmonella typhimurium and Escherichia coli [l 1, 121, and the gene encoding the low-molecular-mass (24 kDa) assimilatory sulfite reductase of Desulfovibrio vulgaris Hildenborough [13]. Gene sequences and regulation of expression were also reported for asrA, asrB and asrC, encoding polypeptides of 4O,31 and 37 kDa, respectively, which form the sulfite reductase of S. typhiniurium [14], capable of reducing sulfite to sulfide under anaerobic conditions. The above indicate a lack of molecular biological information on the dissimilatory sulfite reductases of sulfate-reducing bacteria, in contrast to a wealth of data on the assimilatory enzymes. It appeared, therefore, worthwhle to clone and sequence the genes for desulfoviridin. This project began with the premise that the subunit structure was alp2, and with the expectation of finding an operon of about 2.5 kb, encoding both the a (50 kDa) and p(40 kDa) subunits. However, the cloning of a single gene for an 11-kDa protein reported in this paper presented a puzzle that was solved by the discovery of the y subunit by Pierik et al. [2]. MATERIALS AND METHODS MaterialsAll enzymes used for cloning and dideoxy sequencing were obtained from Pharmacia. Immunoblot staining reagents, nitroblue tetrazolium and 5-bromo-4-chloro-3-indolyl phosphate, and anti-[mouse IgG(H + L)] serum linked to alkaline phosphatase were from Promega. Antibodies against the SDSdenatured c1, p and y desulfoviridin subunits, induced in mice (j? and y) and rabbits (M), were gifts of Drs A. J. Pierik and W.

Novel Genes of the dsr Gene Cluster and Evidence for Close Interaction of Dsr Proteins during Sulfur Oxidation in the Phototrophic Sulfur Bacterium Allochromatium vinosum

“…The sulfite reductase-encoding genes dsrAB can be linked with dsrN and in one case also with dsrC (42,44). dsrC constitutes an independent transcriptional unit in D. vulgaris (36) and is also located apart from dsrAB in the hyperthermophilic archaeal sulfate reducer Ag. fulgidus (40).…”

Purification, crystallization and preliminary crystallographic analysis of a dissimilatory DsrAB sulfite reductase in complex with DsrC

“…Another interesting aspect of Dvir is that it forms a stable complex with a smaller protein of 11 kDa, initially classified as a third subunit of dSiR (Pierik et al, 1992), but later identified as the DsrC protein. DsrC is encoded separately from DsrAB, the two subunits of dSiR and their expression is not coordinately regulated (Karkhoff-Schweizer et al, 1993). It is actually one of the most highly expressed proteins in Desulfovibrio vulgaris Hildenborough, with twice the expression level of DsrAB (Haveman et al, 2003).…”

The Crystal Structure of Desulfovibrio vulgaris Dissimilatory Sulfite Reductase Bound to DsrC Provides Novel Insights into the Mechanism of Sulfate Respiration

“…Initial reports described DsrC as a ␥ subunit of dSiRs present in a stoichiometry of ␣ 2 ␤ 2 ␥ 2 (23). However, the dsrC gene is located separately from dsrAB in several sulfate-reducing organisms, like Desulfovibrio vulgaris Hildenborough, where its expression is not coordinately regulated (24). There are also several dSiRs that do not include DsrC (5, 7), but all organisms that contain the dsrAB genes include also dsrC.…”