CODON USAGE BIAS AND TRANSFER-RNA ABUNDANCE IN DROSOPHILA

Codon usage bias of 1,117 Drosophila melanogaster genes, as well as fe wer D. pseudoobscura and D. virilis genes, was examined from the persp ective of relative abundance of isoaccepting tRNAs and their changes d uring development. We found that each amino acid contributes about equ ally and highly significantly to overall codon usage bias, with the ex ception of Asp which had very low contribution to overall bias. Asp wa s also the only amino acid that did not show a clear preference for on e of its synonymous codons. Synonymous codon usage in Drosophila was c onsistent with ''optimal'' codons deduced from the isoaccepting tRNA a vailability. Interestingly, amino acids whose major isoaccepting tRNAs change during development did not show as strong bias as those with d evelopmentally unchanged tRNA pools. Asp is the only amino acid for wh ich the major isoaccepting tRNAs change between larval and adult stage s. We conclude that synonymous codon usage in Drosophila is well expla ined by tRNA availability and is probably influenced by developmental changes in relative abundance.