Cloning and nucleotide sequence of the carboxynorspermidine decarboxylase gene from Vibrio alginolyticus

The gene (nspC) encoding carboxynorspermidine decarboxylase (CANS DC), the last enzyme in norspermidine biosynthesis, in Vibrio alginolyticus was isolated by immuno-screening and its complete nucleotide sequence was determined. Sequence analysis of the subcloned fragment (2.0 kb) revealed an ORF of 1131 bp encoding a protein of 377 amino acids with a calculated molecular mass of 42008 Da. The sequence of 20 N-terminal amino acids of purified CANS DC was found to be identical to that predicted from the nspC gene. A putative ribosome binding sequence was observed 8 bp upstream from the translation start site (ATG), and promoter- and terminator-like sequences were detected upstream and downstream of the ORF, respectively. Database searches identified no similar proteins, but the deduced amino acid sequence contained a putative pyridoxal 5'-phosphate binding region similar to those of the bacterial meso-2,6-diaminopimelate decarboxylases and eukaryotic ornithine decarboxylases. Another full ORF was found on the opposite strand downstream from the nspC gene. It encoded a protein of 69 amino acids with a calculated molecular mass of 7441 Da, which exhibited some weak similarity to ScrR, a repressor protein of V. alginolyticus, in the helix-turn-helix DNA binding domain, but did not appear to be expressed in the host cells.