Cloning and expression of the luxY gene from Vibrio fischeri strain Y-1 in Escherichia coli and complete amino acid sequence of the yellow fluorescent protein

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Abstract
Vibro fishcheri strain Y-1 (ATCC 33715) emits light with a .lambda.max of 545 nm rather than the 485-nm emission typical of other strains of V. fischeri. The yellow emission is due to the interaction of the enzyme luciferase with a yellow fluorescent protein (YEP). On the basis of the N-terminal amino acid sequence of YFP, a mixed-sequence oligonucleotide probe was synthesized and used to isolate a 1.6-kbp HindIII fragment containing the first 208 bases of the gene that codes for YFP (luxY). Another synthetic oligonucleotide complementary to bases 167-184 of the YFP coding sequence was used to isolate a second (ca. 1.9 kbp) DNA fragment generated by digestion with both EcoRI and ClaI that contained the remainder of the luxY gene. The intact luxY gene, which encoded a 22211-dalton polypeptide composed of 194 amino acid residues, was reconstructed from the two primary clones and is contained within a 765-bp SspI-XhoII fragment. Both strands of the entire luxY coding sequence were determined from the reconstructed gene, while the region surrounding the junction used in the reconstruction was also determined from the original partial clones. As with other genes that have been studied from V. fischeri, the luxY gene was unusually AT-rich. The sequence of luxY did not bear any apparent similarity to any of the sequences contained in the current GenBank database. Escherichia coli containing a plasmid with the luxY gene expresses a protein that reacts with antibody raised to authentic YFP.