Regulation of the mdh-sucCDAB operon in Rhizobium leguminosarum

Abstract

The malate dehydrogenase gene, mdh, from Rhizobium leguminosarum encodes a protein with a molecular weight of 33 590 that associates as a homotetramer. It is a lactate dehydrogenase-like malate dehydrogenase that most closely resembles the protein from the colonial green alga Botryococcus braunii. Malate dehydrogenase from R. leguminosarum has a K m of 74 WM and a V max of 822 Wmol min 31 mg 31 protein for oxaloacetate, while the K m for malate is 3.6 mM and the V max 62 Wmol min 31 mg 31 protein. Downstream of mdh are sucCDAB, which encode succinyl-CoA synthetase (sucCD) and the E1 and E2 components of the K-ketoglutarate dehydrogenase complex (sucAB). Complementation and LacZ fusion analysis indicates that there is a common promoter for the mdh-suc genes. Mutation of downstream genes in the mdh-suc operon increases transcription 7-fold from the mdh promoter. The transcriptional coupling of mdh and sucCDAB is likely to be important in the regulation of carbon and nitrogen metabolism in bacteroids. ß

Functional and Molecular Characterization of the Lpda2 Gene in Sinorhizobium Meliloti

“…The higher activity of MDH might be a response to the increased quantities of 2-Oxoglutarate, or some other related compounds or metabolites that accumulate in the cell blocked in OGD (Gao and Jiang, 2002), in an attempt to remove the blockage by increasing the transcription of the OGD genes. As a consequence the mdh is upregulated because it is cotranscriped from the same promoter as the sucAB genes in both R. leguminosarum and S. meliloti, the situation that was not encountered in B. japonicum (Walshaw et al, 1997) which expresses monocistronic mdh from a separate promoter (Poole et al, 1999). As OGD activity was significantly abolished in the LpdA2 mutant strain, it seems that neither LpdA1 nor LpdA3 can replace it.…”

Molecular Studies for Putative Promoter Activity in mdh sucCDAB Operon in Sinorhizobium meliloti

“…Sinorhizobium meliloti, has two main operons encode genes of the Tricarboxylic Acid Cycle (TCA), (Poole et al, 1999). Malate dehydrogenase (MDH) is the first gene in an operon that also encodes the two subunits of succinyl-CoA synthetase (sucCD) and two of the three subunits of 2-oxoglutarate dehydrogenase (OGD) namely (sucAB), thus, has the structure mdh-sucCDAB.…”