Evolution of Retrotransposable Elements
نویسندگان
چکیده
ABC Fax + 41 61 306 12 34 E-mail [email protected] www.karger.com © 2005 S. Karger AG, Basel 1424–8581/05/1104–0392$22.00/0 Accessible online at: www.karger.com/cgr Abstract. Eukaryotic and prokaryotic genomes encode either Type I or Type II Ribonuclease H (RNH) which is important for processing RNA primers that prime DNA replication in almost all organisms. This review highlights the important role that Type I RNH plays in the life cycle of many retroelements, and its utility in tracing early events in retroelement evolution. Many retroelements utilize host genome-encoded RNH, but several lineages of retroelements, including some non-LTR retroposons and all LTR retrotransposons, encode their own RNH domains. Examination of these RNH domains suggests that all LTR retrotransposons acquired an enzymatically weak RNH domain that is missing an important catalytic residue found in all other RNH enzymes. We propose that this reduced activity is essential to ensure correct processing of the polypurine tract (PPT), which is an important step in the life cycle of these retrotransposons. Vertebrate retroviruses appear to have reacquired their RNH domains, which are catalytically more active, but their ancestral RNH domains (found in other LTR retrotransposons) have degenerated to give rise to the tether domains unique to vertebrate retroviruses. The tether domain may serve to control the more active RNH domain of vertebrate retroviruses. Phylogenetic analysis of the RNH domains is also useful to “date” the relative ages of LTR and nonLTR retroelements. It appears that all LTR retrotransposons are as old as, or younger than, the “youngest” lineages of nonLTR retroelements, suggesting that LTR retrotransposons arose late in eukaryotes.
منابع مشابه
Retrotransposable elements and human disease.
Nearly 50% of the human genome is composed of fossils from the remains of past transposable element duplication. Mobilization continues in the genomes of extant humans but is now restricted to retrotransposons, a class of mobile elements that move via a copy and paste mechanism. Currently active retrotransposable elements include Long INterspersed Elements (LINEs), Short INterspersed Elements (...
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ABC Fax + 41 61 306 12 34 E-mail [email protected] www.karger.com © 2005 S. Karger AG, Basel 1424–8581/05/1104–0426$22.00/0 Accessible online at: www.karger.com/cgr Abstract. Retrotransposable elements and transposons are generally both found in most eukaryotes. These two classes of elements are usually distinguished on the basis of their differing mechanisms of transposition. However, their res...
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