Reverse transcription of retroviruses and LTR retrotransposons

Abstract

Retroelements are mobile genetic entities that replicate via reverse transcription of a template RNA. A key component to the life cycle of these elements is the enzyme reverse transcriptase (RT), which copies the single-stranded genomic RNA of the element into a linear double-stranded DNA that is ultimately integrated into the host genome by the element-encoded integrase. RT is a multifunctionnal enzyme which possesses RNA-dependent and DNA-dependent DNA polymerase activities as well as RNase H activity that specifically degrades the RNA strand of RNA-DNA duplexes. At some stages of the replication a strand-displacement activity of RT is also necessary. All activities are essential for the conversion of single-stranded genomic RNA into the double-stranded preintegrative DNA. This review focuses on the role of RT in the different steps of the replication process of retroelements. The features of retrotransposon replication which differ from the retroviral ones will be emphasized. In a second part of the review, the biochemical and enzymatic properties of two newly characterized retrotransposon RTs will be described. The role of the integrase domain in reverse transcriptase activity of some retroviral and retrotransposon RTs will be discussed.

Highly abundant pea LTR retrotransposon Ogre is constitutively transcribed and partially spliced

“…Their LTR sequences are hundreds to several thousand bases in length, carry regions important for transcription (promoter, polyadenylation signal), and play a key role in a strand transfer occurring during the element's reverse transcription (Temin, 1981;Kumar and Bennetzen, 1999;Bennetzen, 2000;Wilhelm and Wilhelm, 2001). In their vicinity there are additional sequences important for element replication: the primer binding site (PBS, complementary to the 3 end of certain tRNA) downstream of the left LTR, and the polypurine tract (PPT) upstream of the right LTR (Temin, 1981;Kumar and Bennetzen, 1999;Wilhelm and Wilhelm, 2001). The region between the two LTRs contains two genes, gag and pol, encoding all proteins necessary for the element's transposition (Boeke and Stoye et al, 1997).…”

Reduced Basal Transcriptional Activity of Central Nervous System-Derived HIV Type 1 Long Terminal Repeats

“…2,3 In addition, the LTR is involved in reverse transcription of the RNA genome, integration of the provirus into the host cell genome, and the generation of viral genomes for virus assembly. 4,5 The HIV-1 provirus contains two identical LTRs, each comprising unique 3¢ (U3), the flanking R, and unique 5¢ (U5) regions at either end. 5 The U3 region is further subdivided into modulatory, enhancer, and core segments according to transcription factor binding sites that populate the LTR and their impact on LTR activity and viral gene expression.…”

Retrotransposons and their Role in Plant—Genome Evolution

“…In gypsy-like elements in contradiction to copia-like elements, the integrase (IN) is at the end of the open reading frame. LTR retrotransposons and closely related infectious and endogenous retroviruses (97) have similar intracellular life cycles and major encoded proteins (gag, which codes proteins for virus particles, and pol, which encodes the enzymatic activities for replication) (54), but retrotransposons lack a domain env, encoding an envelope glycoprotein critical for infectivity. The encoded by retroviruses envelope glycoproteins associate with cell membranes and facilitate the budding of viral core particles from infected cells.…”