Subfamilies of CR1 non-LTR retrotransposons have different 5 ' UTR sequences but are otherwise conserved

CR1 elements and CR1-related (CR1-like) elements are a novel family of non- LTR retrotransposons that are found in all vertebrates (reptilia, amphibia, fish, and mammals), whereas more distantly related elements are found in s everal invertebrate species. CRI elements have several features that distin guish them from other non-LTR retrotransposons. Most notably, their 3' term ini lack a polyadenylic acid (poly A) tail and instead contain 2-4 copies o f a unique 8 bp repeat. CR1 elements are present at similar to 100.000 copi es in the chicken genome. The vast majority of these elements are severely 5' truncated and mutated; however, six subfamilies (CR1-A through CR1-F) ar e resolved by sequence comparisons. One of these subfamilies (i.e. CR1-B) p reviously was analyzed in detail. In the present study, we identified sever al full-length elements from the CR1-F subfamily. Although regions within t he open reading frames and 3' untranslated regions of CR1-F and CR1-B eleme nts ore well conserved, their respective 5' untranslated regions are unrela ted. Thus, our results suggest that new CR1 subfamilies form when elements with intact open reading frames acquire new 5'UTRs, which could, in princip le, function as promoters. (C) 2001 Elsevier Science B.V. All rights reserv ed.