Long terminal repeat
DNA sequence
A long terminal repeat (LTR) is a pair of identical sequences of DNA, several hundred base pairs long, which occur in eukaryotic genomes on either end of a series of genes or pseudogenes that form a retrotransposon or an endogenous retrovirus or a retroviral provirus. All retroviral genomes are flanked by LTRs, while there are some retrotransposons without LTRs. Typically, an element flanked by a pair of LTRs will encode a reverse transcriptase and an integrase, allowing the element to be copied and inserted at a different location of the genome. Copies of such an LTR-flanked element can often be found hundreds or thousands of times in a genome. LTR retrotransposons comprise about 8% of the human genome.
The first LTR sequences were found by A.P. Czernilofsky and J. Shine in 1977 and 1980.
Transcription
The LTR-flanked sequences are partially transcribed into an RNA intermediate, followed by reverse transcription into complementary DNA (cDNA) and ultimately dsDNA (double-stranded DNA) with full LTRs. The LTRs then mediate integration of the DNA via an LTR specific integrase into another region of the host chromosome.
Retroviruses such as human immunodeficiency virus (HIV) use this basic mechanism.
Dating retroviral insertions
As 5' and 3' LTRs are identical upon insertion, the difference between paired LTRs can be used to estimate the age of ancient retroviral insertions.
Begin with the source’s own compact description: “Long terminal repeat” is dNA sequence. The dossier treats that line as a proposition to test through Long, terminal and repeat, not as a finished interpretation.
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The phrase “dNA sequence” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 14, 2026. The linked authority identifier is Q1869477. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1977 and 1980.
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This entry incorporates text from “Long terminal repeat” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.