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Related Concept Videos

Retroviruses02:33

Retroviruses

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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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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.
The internal coding region of LTR retrotransposons and their mechanism of transposition closely resembles a...
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Non-LTR Retrotransposons03:18

Non-LTR Retrotransposons

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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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Retrovirus Life Cycles01:10

Retrovirus Life Cycles

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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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Mechanisms of Retrovirus-induced Cancers01:51

Mechanisms of Retrovirus-induced Cancers

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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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Size and Structure of Viral Genomes01:26

Size and Structure of Viral Genomes

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Viral genomes exhibit remarkable diversity in size, structure, and composition, influencing their replication strategies and interactions with host cells. These genomes consist of either DNA or RNA and may be linear or circular. Additionally, they can be single-stranded or double-stranded, with each configuration affecting how the virus propagates within a host. RNA viruses, for instance, generally have smaller genomes than DNA viruses, a factor that contributes to their high mutation rates and...
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Related Experiment Video

Updated: Sep 30, 2025

Analysis of LINE-1 Retrotransposition at the Single Nucleus Level
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Analysis of LINE-1 Retrotransposition at the Single Nucleus Level

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A Missing Link between Retrotransposons and Retroviruses.

Jianhua Wang1, Guan-Zhu Han1

  • 1Jiangsu Key Laboratory for Microbes and Functional Genomics, College of Life Sciences, Nanjing Normal Universitygrid.260474.3, Nanjing, Jiangsu, China.

Mbio
|March 15, 2022
PubMed
Summary
This summary is machine-generated.

Scientists discovered novel Odin retrotransposons in sea anemones. These elements bridge the evolutionary gap between retrotransposons and retroviruses, offering new insights into viral origins.

Keywords:
Comparative genomicsevolutionphylogenetic analysisretrotransposonsretroviruses

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RNA Next-Generation Sequencing and a Bioinformatics Pipeline to Identify Expressed LINE-1s at the Locus-Specific Level
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Area of Science:

  • Evolutionary Biology
  • Virology
  • Genomics

Background:

  • The evolutionary origins of retroviruses are poorly understood.
  • Existing Ty3/Gypsy retrotransposons are only distantly related to retroviruses.
  • Retroviruses and some plant elements share dual RNase H and env genes.

Purpose of the Study:

  • To investigate the deep evolutionary history of retroviruses.
  • To identify novel genetic elements that may illuminate retroviral origins.
  • To understand the relationship between retrotransposons and retroviruses.

Main Methods:

  • Genome sequencing of eight sea anemone species (order Actinaria).
  • Phylogenetic analyses using reverse transcriptase, RNase H, and integrase domains.
  • Comparative genomic analysis of retrotransposon and retroviral features.

Main Results:

  • Discovery of a novel retrotransposon lineage, Odin retrotransposons, in sea anemones.
  • Odin retrotransposons possess a dual RNase H domain but lack an env gene.
  • Phylogenetic analyses place Odin retrotransposons as sister to lokiretroviruses, and both as sister to canonical retroviruses.

Conclusions:

  • Odin retrotransposons represent a crucial intermediate in retroviral evolution.
  • The findings suggest lokiretroviruses and canonical retroviruses may be distinct families.
  • This discovery provides a framework for understanding retroviral and LTR retrotransposon deep evolution.