Comparison of Base Composition and Codon Usage in Insect Mitochondrial Genomes

Insects, the most biodiverse taxonomic group, have high AT content in their mitochondrial genomes. Although codon usage tends to be AT-rich, base composition and codon usage of mitochondrial genomes may vary among taxa. Thus, we compare base composition and codon usage patterns of 49 insect mitochondrial genomes. For protei coding genes, AT content is as high as 80% in the Hymenoptera and Lepidoptera and as low as 72% in the Orthopotera. The AT content is high at positions I and 3, but A content is low at position 2. A close correlation occurs between codon usage and tRNA abundance in nuclear genomes. Optimal codons can pair well with the anticodons of the most abundant tRNAs. One tRNA gene translates a synonymous codon family in vertebrate mitochondrial genomes and these tRNA anticodons can pair with optimal codons. However, optimal codons can-not pair with anticodons in mtDNA of Cochliomyia hominivorax (Diptera: Calliphoridae). Ten optimal codons cannot pair with tRNA anticodons in all 49 insect mitochondrial genomes; non-optimal codon-anticodon usage is common and codon usage is not influenced by tRNA abundance.