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GC ratio requirements drove the divergence of bacterial bioluminescence proteins Timothy C. Johnston*1; James R Cox2 (1) Department of Biological Sciences, Murray, KY 42071, USA; (2) Department of Chemistry, Murray State University, Murray, KY 42071      *(tim.johnston@murraystate.edu) We compared the codon usage of the luxA and luxB genes of bioluminescent bacteria and found that usage at the third position of codons conforms to the GC ratios reported for these organisms. For example, V. fischeri and V. harveyi have genomic GC ratios of 38.9% and 46.4% respectively and V. fischeri uses 30% more A or U at the third position than V. harveyi. In addition to influencing codon choice, GC ratio has influenced amino acid choice in the encoded proteins. Amino acids encoded by G or C in the first and second positions are less prevalent in the proteins of V. fischeri than those of V. harveyi. Conversely, amino acids encoded by A or U in any position are more abundant in V. fischeri proteins. We have aligned the luciferase subunits and compared the amino acid choice at positions that are not conserved and found that even though first and second position choice has been made to include more codons with A or U in V. fischeri, the conformational preferences of the amino acids in the proteins are conserved. We conclude that the divergence of the luciferases of bacteria is driven, in part, by the requirement of a GC ratio that is optimum for that species, while conserving the structure and activity of the proteins. [Talk: johnston.timoth.05061]

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