Fm. Garcia-rodriguez et al., Characterization of the Sinorhizobium meliloti genes encoding a functionaldihydrodipicolinate synthase (dapA) and dihydrodipicolinate reductase (dapB), ARCH MICROB, 173(5-6), 2000, pp. 438-444
In bacteria, the known pathways for diaminopimelate (DAP) and lysine biosyn
thesis share two key enzymes, dihydrodipicolinate synthase and dihydrodipic
olinate reductase, encoded by the dapA and dapB genes, respectively. In rhi
zobia, these genes have not yet been genetically characterized. In this wor
k, by sequence analysis, we identified two divergent open reading frames on
the 140-MDa plasmid pRmeGR4b of Sinorhizobium meliloti strain GR4. Termed
dapA and dapB, these encode products which show significant sequence simila
rities to DapA and DapB proteins, respectively. Escherichia coli DAP auxotr
ophs (dapA and dapB mutants) could be complemented with the pRmeGR4b dapA a
nd dapB genes, indicating that these genes code for functional dihydrodipic
olinate synthase and dihydrodipicolinate reductase, respectively. Reverse-t
ranscriptase PCR analyses and P-galactosidase assays using transcriptional
dapA-lacZ and dapB-lacZ fusions suggest that these genes are constitutively
expressed in S. meliloti. The dapA and dapB genes are not widely distribut
ed in S. meliloti and appear to be specific for strains carrying pRmeGR4b-t
ype plasmids.