Transfer RNA（tRNA）genes in higher eukaryotes are well known for their strict intron position which is only located at nucleotide position 37/38（so-called canonical position). On the other hand, many archaeal tRNA genes possess single and multiple introns located at other positions（non-canonical positions). Although these disrupted tRNAs are considered as key evidence to elucidate the origin and evolution of tRNA, its generality and evolutionary impact in eukaryotes are not fully understood. Previously, we have developed a computational method to predict disrupted tRNAs in eukaryotes by extracting genomic regions possessing tRNA-like sequences based on blastn search. Using this method, we successfully predicted total 77 novel non-canonical intron-containing tRNA（ni-tRNA）candidates from 44 eukaryotic genomes. Besides, in several Caenorhabditis（worm）genomes, many unusual variable arm containing tRNAs（uv-tRNA）have been predicted but interestingly their anticodons corresponded to neither leucine nor serine, known as common V-arm containing tRNAs. To confirm the expression of these newly predicted tRNA genes, we performed RT-PCR and DNA sequencing analysis of three ni-tRNAs and five uv-tRNAs in Caenorhabditis elegans. As a result, while expression of uv-tRNAGly and uv-tRNAIle were observed, no expression was detected for ni-tRNA. Further sequence and phylogenetic analysis revealed that uv-tRNA seems to be evolved from tRNASer / tRNALeu rather than gene duplication of synonymous tRNAs. Possible functions of these uv-tRNAs are discussed.

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