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Sequence Analysis of the Start Region of Lepidopteran Mitochondrial COI Gene
Invertebrate mitochondrial genome contains 13 protein-coding genes and major start codons for them are ATA (Met) and ATG (Met). However, alternative start codons such as ATT (Ile), ATC (Ile), TTG (Leu), and GTG (Val) also have been suggested from a diverse organism. Approximately 120 complete mitochondrial genome reported showed that the start codon for COI gene evidences an array of diverse designation of COI start codon such as typical ATN, tetranucleotide TTAG and ATAA, newly proposed AAT and AAC and so on. In the case of Lepidoptera, many completely sequenced species showed no typical start codon at the start context of COI and even within the neighboring tRNATyr. In order to clarify, we newly sequenced the beginning context of COI gene, encompassing the neighboring tRNATyr and start region of COI gene from 39 species belonging to eight lepidopteran families. We found the newly sequenced 39 species and 14 available complete lepidopteran mitochondrial genomes all possessed CGA (arginine), which is the first non-overlapping in-frame codon in COI gene. Furthermore, this CGA is highly well aligned in terms of both nucleotide and amin o acid sequences with neighboring region. Thus, the CGA (arginine) may be synapomorphic character for Lepidoptera, functionally constrained. We, therefore, propose the CGA sequence as the start codon for COI gene in lepidopteran insects.
