Nucleotide sequence of theLuxCgene and the upstream DNA from the bioluminescent system ofVibrio harveyi

The nucleotide sequence of the luxC gene (1431 bp) and the upstream DNA (1049 bp) of the luminescent bacterium Vibrio harveyi has been determined. The luxC gene can be translated into a polypeptide of 55 kDa in excellent agreement with the molecular mass of the reductase polypeptide required for synthesis of the aldehyde substrate for the bioluminescent reaction. Analyses of codon usage showed a high frequency (1.9%) of the isoleucine codon, AUA, in the luxC gene compared to that found in Escherichia coli genes (0.2%) and its absence in the luxA, B and D genes. The low G/C content of the luxC gene and upstream DNA (38-39%) compared to that found in the other lux genes of V. harveyi (45%) was primarily due to a stretch of 500 nucleotides with only a 24% G/C content, extending from 200 bp inside lux C to 300 bp upstream. Moreover, an open reading frame did not extend for more than 48 codons between the luxC gene and 600 bp upstream at which point a gene transcribed in the opposite direction started. As the lux system in the luminescent bacterium, V. fischeri, contains a regulatory gene immediately upstream of luxC transcribed in the same direction, these results show that the organization and regulation of the lux genes have diverged in different luminescent bacteria.