Meeting Abstract

P1.84A  Monday, Jan. 4  Extensive tRNA editing in mitochondrial genomes of Onychophora SEGOVIA, Romulo*; WALKER, Pett; TREWICK, Steve; GLEASON , Dianne; LAVROV, Dennis; Iowa State University; Iowa State University; Massey University; EcoGene New Zealand; Iowa State University; Massey University rsegovia@iastate.edu

One of the most difficult tasks in annotating animal mitochondrial genomes is identification of transfer RNA genes. This is because these genes underwent degenerative evolution and lost most of the features characteristic of “standard” tRNAs. Furthermore, in some lineages, maturation of tRNA genes involves RNA editing. Despite the fact that “absence of evidence is not evidence of absence”, the inability to identify some tRNA genes have led to repeated claims that these genes are absent from the genomes. As an example, in a recent paper Podsiadlowski et al. have claimed that onychophoran Epiperipatus biolleyi lacks all tRNA genes for 4-fold degenerate codons and that this absence “raises the fundamental question of whether there are any differences in the recognition mechanisms” between tRNAs for 2-fold and 4-fold degenerate codons. However, we have previously sequenced mtDNA from the same species and identified all 22 tRNAs characteristic for animal mtDNA. To check whether genes for 4-fold degenerate tRNAs are indeed absent from onychophoran mtDNA we checked for the presence of these tRNAs on RNA level by the RT-PCR approach. We found that tRNA genes for 4-fold degenerate codons are present in onychophoran mtDNA but that all tRNA genes undergo extensive tRNA editing at the 3’ end. This editing not only repairs the mismatched pairs of nucleotides in the 3’-ends of the acceptor stems by forming Watson-Crick base pairs in a 5’-end template-dependent editing system, but also edits many nucleotides in the TYC arm. Further study of mt-tRNA gene in the onychophoran Peripatoides sympatrica from New Zealand suggests that this editing mechanism evolved early in the evolution of the group and has been retained for at least 100 MY.