Sequence of the sodium ion pump oxaloacetate decarboxylase from Salmonella typhimurium

A genomic library of Salmonella typhimurium DNA was constructed in the lambda-phage EMBL3 and screened by immunoblotting for expression of the oxaloacetate decarboxylase alpha-subunit. After subcloning on plasmids the entire sequence of the oxaloacetate decarboxylase was determined. The genes encoding subunits gamma (oadG), alpha (oadA), and beta (oadB) of the decarboxylase are clustered on the chromosome in that order. A typical consensus sequence of a promoter is not found upstream of the oadG gene, but putative ribosome binding regions can be identified before each subunit gene. The amino acid sequences are highly homologous to those of oxaloacetate decarboxylase from Klebsiella pneumoniae with 71% identity between the gamma-subunits, 92% identity between the alpha-subunits, and 93% identity between the beta-subunits. The homology between the corresponding beta-subunits appeared to exist only between the 312 N-terminal amino acid residues. It was shown that a cloning artifact has occurred during DNA sequence determination of the beta-subunit from K. pneumoniae and has led to erroneous results. The sequence of this polypeptide is corrected in the Appendix to this paper. A plasmid encoding the three oad genes and that for the anaerobic citrate carrier (citS) was cloned from the chromosomal DNA and used for sequence determination.