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Related Concept Videos

LTR Retrotransposons03:08

LTR Retrotransposons

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LTR retrotransposons are class I transposable elements with long terminal repeats flanking an internal coding region. These elements are less abundant in mammals compared to other class I transposable elements. About 8 percent of human genomic DNA comprises LTR retrotransposons. Some of the common examples of LTR retrotransposons are Ty elements in yeast and Copia elements in Drosophila.
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Retroviruses and retrotransposons both insert copies of their genetic elements into the genome of the host cell. Thus, the viral genes are passed on when the host genome is replicated or translated. A typical retroviral DNA sequence contains 3-4 genes that encode the different proteins required for its structural assembly and function as a molecular parasite. This DNA is transcribed into a single mRNA, which is very similar in structure to conventional mRNAs, i.e., it is capped at the 5’...
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Retroviruses have a single-stranded RNA genome that undergoes a special form of replication. Once the retrovirus has entered the host cell, an enzyme called reverse transcriptase synthesizes double-stranded DNA from the retroviral RNA genome. This DNA copy of the genome is then integrated into the host’s genome inside the nucleus via an enzyme called integrase. Consequently, the retroviral genome is transcribed into RNA whenever the host’s genome is transcribed, allowing the...
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Retroviruses are RNA viruses that have been shown to cause cancers in diverse species, including chickens, mice, cats, and monkeys. The RNA genomes of these viruses are first reverse-transcribed into single and then double-stranded DNA (dsDNA) copies. This dsDNA called proviral DNA then integrates into the host genome. Subsequently, the host cell transcribes the proviral DNA in concert with the chromosomal DNA. This leads to the production of viral RNA and proteins that assemble at the host...
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As the name suggests, non-LTR retrotransposons lack the long terminal repeats characteristic of the LTR retrotransposons. Additionally, both LTR and non-LTR retrotransposons use distinct mechanisms of mobilization. Non-LTR retrotransposons are further divided into two classes - Long interspersed nuclear elements (LINEs) and short interspersed nuclear elements (SINEs), both of which occur abundantly in most mammals, including humans. Some of the active non-LTR retrotransposons in humans are L1...
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Mammalian Endogenous Retroviruses.

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Endogenous retroviruses (ERVs) are ancient genetic elements comprising up to 10% of mammalian genomes. While some ERVs cause disease, others have been repurposed for essential host functions like placental development.

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Area of Science:

  • Genomics
  • Molecular Biology
  • Evolutionary Biology

Background:

  • Over 40% of mammalian genomes originate from reverse transcription.
  • Endogenous retroviruses (ERVs) are retrotransposed sequences with long terminal repeats (LTRs).
  • ERV sequences constitute 8-10% of human and mouse genomes, varying in age and activity.

Purpose of the Study:

  • To describe the discovery, classification, and origins of ERVs in mammals.
  • To examine cellular mechanisms controlling ERV expression.
  • To discuss the dual role of ERVs in disease and host function.

Main Methods:

  • Review of existing literature on ERVs.
  • Analysis of genomic sequences and evolutionary history.
  • Examination of cellular control mechanisms and functional domestication.

Main Results:

  • ERVs have diverse origins, predating mammalian divergence to active elements.
  • Cellular mechanisms have evolved to suppress ERV expression.
  • ERV proteins have been domesticated for crucial host functions, e.g., placental development.
  • ERV LTRs have been repeatedly co-opted for gene regulation.

Conclusions:

  • ERVs represent a significant and dynamic component of mammalian genomes.
  • While potentially pathogenic, ERVs can be neutralized or co-opted for beneficial host roles.
  • The regulatory potential of ERV LTRs has been a key evolutionary innovation.