Selenocysteine tRNA identification in the model organisms Dictyostelium discoideum and Tetrahymena thermophila

Characterizing See tRNAs that decode UGA provides one of the most direct and easiest means of determining whether an organism possesses the ability to insert selenocysteine (See) into protein. Herein, we used a combination of two techniques, computational to identify Sec tRNA genes and RT-PCR to sequence the gene products, to unequivocally demonstrate that two widely studied, model protozoans, Dictyostelium discoideum and Tetrahymena thermophila, encode See tRNA in their genomes. The advantage of using both procedures is that computationally we could easily detect potential See tRNA genes and then confirm by sequencing that the See tRNA was present in the tRNA population, and thus the identified gene was not a pseudogene. See tRNAs from both organisms decode UGA. T thermophila See tRNA, like all other sequenced See tRNAs, is 90 nucleotides in length, while that from D. discoideum is 91 nucleotides long making it the longest eukaryotic sequenced to date. Evolutionary analyses of known See tRNAs reveal the two forms identified herein are the most divergent eukaryotic See tRNAs thus far sequenced. (C) 2005 Elsevier Inc. All rights reserved.