THE RTE CLASS OF NON-LTR RETROTRANSPOSONS IS WIDELY DISTRIBUTED IN ANIMALS AND IS THE ORIGIN OF MANY SINES

RTE-1 is a non-long-terminal-repeat (non-LTR) retrotransposable elemen t first found in the Caenorhabditis elegans genome. It encodes a 1,024 -amino-acid open reading frame (ORF) containing both apurinic-apyrimid ic endonuclease and reverse-transcriptase domains. A possible first OR F of only 43 amino acids overlaps with the larger ORF and may be the s ite of translation initiation. Database searches and phylogenetic anal ysis indicate that representatives of the RTE clade of non-LTR retrotr ansposons are found in the bovine and sheep genomes of mammals and in the silkmoth and mosquito genomes of insects. In addition, the previou sly identified SINEs, Art2 and Pst, from ruminate and viper genomes ar e shown to be truncated RTE-like retrotransposable elements. RTE-deriv ed SINE elements are also found in mollusc and flatworm genomes. Membe rs of the RTE clade are characterized by unusually short 3' untranslat ed regions that are predominantly composed of AT-rich trimer, tetramer , and/or pentamer repeats. This study establishes RTE as a very widesp read clade of non-LTR retrotransposons. RTE represents the third disti nct class of non-LTR retrotransposons in the vertebrate lineage (after Line 1 elements in mammals and CRI elements in birds and reptiles).