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Related Concept Videos

Telomeres and Telomerase02:41

Telomeres and Telomerase

In eukaryotic DNA replication, a single-stranded DNA fragment remains at the end of a chromosome after the removal of the final primer. This section of DNA cannot be replicated in the same manner as the rest of the strand because there is no 3’ end to which the newly synthesized DNA can attach. This non-replicated fragment results in gradual loss of the chromosomal DNA during each cell duplication. Additionally, it can induce a DNA damage response by enzymes that recognize single-stranded DNA.
Telomeres and Telomerase02:41

Telomeres and Telomerase

In eukaryotic DNA replication, a single-stranded DNA fragment remains at the end of a chromosome after the removal of the final primer. This section of DNA cannot be replicated in the same manner as the rest of the strand because there is no 3’ end to which the newly synthesized DNA can attach. This non-replicated fragment results in gradual loss of the chromosomal DNA during each cell duplication. Additionally, it can induce a DNA damage response by enzymes that recognize single-stranded DNA.
LTR Retrotransposons03:08

LTR Retrotransposons

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...
Non-LTR Retrotransposons03:18

Non-LTR Retrotransposons

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...
Replication in Eukaryotes02:31

Replication in Eukaryotes

Overview
Replication in Eukaryotes01:29

Replication in Eukaryotes

In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before cell division, so there are many proteins that fulfill specialized roles in the replication process. Replication occurs in three phases: initiation, elongation, and termination, and ends with two complete sets of chromosomes in the nucleus.
Many Proteins Orchestrate Replication at the Origin
Eukaryotic replication follows many of the same...

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Related Experiment Video

Updated: May 29, 2026

Semi-quantitative Detection of RNA-dependent RNA Polymerase Activity of Human Telomerase Reverse Transcriptase Protein
08:26

Semi-quantitative Detection of RNA-dependent RNA Polymerase Activity of Human Telomerase Reverse Transcriptase Protein

Published on: June 12, 2018

Similarities between long interspersed element-1 (LINE-1) reverse transcriptase and telomerase.

Huira C Kopera1, John B Moldovan, Tammy A Morrish

  • 1Department of Human Genetics, University of Michigan Medical School, Ann Arbor, MI 48109-5618, USA. chongh@umich.edu

Proceedings of the National Academy of Sciences of the United States of America
|September 24, 2011
PubMed
Summary

Long interspersed element-1 (LINE-1) retrotransposons can use telomere-like sequences to initiate reverse transcription via an endonuclease-independent pathway. This process, observed in vitro, highlights similarities between LINE-1 retrotransposition and telomerase activity.

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Published on: June 12, 2018

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Analysis of LINE-1 Retrotransposition at the Single Nucleus Level
11:52

Analysis of LINE-1 Retrotransposition at the Single Nucleus Level

Published on: April 23, 2016

Area of Science:

  • Molecular Biology
  • Genetics
  • Cell Biology

Background:

  • Long interspersed element-1 (LINE-1 or L1) retrotransposons utilize target-site primed reverse transcription for mobilization.
  • An alternative endonuclease-independent (ENi) pathway for L1 retrotransposition exists, particularly in cells with defects in DNA repair pathways like nonhomologous end-joining.
  • ENi L1 retrotransposition has been observed to target dysfunctional telomeres in specific cellular contexts.

Purpose of the Study:

  • To investigate the mechanism of endonuclease-independent (ENi) L1 retrotransposition.
  • To determine if L1 ribonucleoprotein particles can use telomere-like structures as primers for reverse transcription.
  • To elucidate the role of ORF1p in ENi L1 retrotransposition at telomeres.

Main Methods:

  • In vitro assay to detect L1 reverse transcriptase activity.
  • Use of oligonucleotide adapters mimicking telomeric ends.
  • Analysis of endonuclease-defective L1 ribonucleoprotein particles.
  • Assessment of ORF1p requirement in ENi retrotransposition.

Main Results:

  • Wild-type and endonuclease-defective L1 ribonucleoprotein particles can use telomere-mimicking oligonucleotide adapters to initiate L1 mRNA reverse transcription.
  • These ribonucleoprotein particles possess nuclease activity to process the adapter primers prior to reverse transcription.
  • ORF1p is not essential for ENi L1 retrotransposition events occurring at dysfunctional telomeres.

Conclusions:

  • The findings demonstrate that L1 retrotransposons can employ telomere-like sequences as primers for reverse transcription through an endonuclease-independent mechanism.
  • The observed nuclease activity and primer processing further support the analogy between ENi L1 retrotransposition and telomerase.
  • These results deepen the understanding of L1 retrotransposition mechanisms and their potential interactions with telomeres and DNA repair pathways.