The complete mitochondrial DNA sequence of the basal Hexapod Tetrodontophora bielanensis: Evidence for heteroplasmy and tRNA translocations

We present the complete 15,455-nt mitochondrial DNA sequence of the springt ail Tetrodontophora bielanensis (Arthropoda, Hexapoda, Collembola). The gen e content is typical of most metazoans, with 13 protein-coding genes (PCGs) , 2 genes encoding for ribosomal RNA subunits, and 22 tRNA genes. The nucle otide sequence shows the well-known A+T bias typical of insect mtDNA; its A +T content is lower (72.7%) than that observed in other insect species, but still higher than that in other arthropodan taxa. The bias appears to be u niform across the whole molecule, unlike other insect taxa, which show incr eased A+T content in the so-called A+T-rich region. However, the bias is sl ightly higher in the third codon positions of the PCGs (81.4%). Anomalous i nitiation codons have been observed in the nad2 and the cox1 genes. In the latter, the ATTTAA hexanucleotide is suggested to be involved in the initia tion signaling. All tRNAs could be folded into the typical cloverleaf secon dary structure, but the tRNA for cysteine appears to be missing the DHU arm . Long tandemly repeated regions (193 nt) were found in the A+T-rich region , which in turn was shown to have the possibility of forming a complex arra y of secondary structures. One of these structures encompassed the junction between the repeats. The A+T-rich region was also interesting in that it s howed heteroplasmy in the number of repeats. Three haplotypes were found, p ossessing 2, 3, and 4 identical repeats, respectively. The order of protein coding and rRNA genes in the molecule was determined and was identical to that of all insects studied so far. However, two tRNA translocations were f ound which were unprecedented among Arthropoda. These involved the a-ne, wh ich was found between the rrnS and the A+T-rich region, and the trnS(ucn), which was located between trnM and trnI. A preliminary phylogenetic analysi s based on the amino acid sequence of the PCGs failed to find support for t he monophyly of Hexapoda.