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Telomeres and Telomerase

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 Telomerase

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 Retrotransposons

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 Retrotransposons

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...

Polytene Chromosomes

Polytene Chromosomes

Polytene chromosomes are giant interphase chromosomes with several DNA strands placed side by side. They were discovered in the year 1881 by Balbiani in salivary glands, intestine, muscles, malpighian tubules, and hypoderm of larvae Chironomus plumosus. Hence, these are also called "Salivary gland chromosomes." These are found in insects of the order Diptera and Collembola; in certain organs of mammals; and synergids, antipodes of flowering plants. Polytene chromosomes are also regularly...

Polytene Chromosomes

Polytene Chromosomes

Polytene chromosomes are giant interphase chromosomes with several DNA strands placed side by side. They were discovered in the year 1881 by Balbiani in salivary glands, intestine, muscles, malpighian tubules, and hypoderm of larvae Chironomus plumosus. Hence, these are also called "Salivary gland chromosomes." These are found in insects of the order Diptera and Collembola; in certain organs of mammals; and synergids, antipodes of flowering plants. Polytene chromosomes are also regularly...

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Related Experiment Video

Updated: May 20, 2026

Analyzing Telomeric Protein-DNA Interactions Using Single-Molecule Magnetic Tweezers

Analyzing Telomeric Protein-DNA Interactions Using Single-Molecule Magnetic Tweezers

Published on: August 30, 2024

A TRF1-controlled common fragile site containing interstitial telomeric sequences.

Nazario Bosco¹, Titia de Lange

¹Laboratory for Cell Biology and Genetics, The Rockefeller University, Box 159, 1230 York Avenue, New York, NY 10065, USA.

|July 14, 2012

Summary

Telomeres, the protective caps on chromosomes, can become fragile sites. This study reveals that telomeric DNA sequences inherently cause fragility, independent of their location, and identifies a specific protein that stabilizes these sites.

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Last Updated: May 20, 2026

Analyzing Telomeric Protein-DNA Interactions Using Single-Molecule Magnetic Tweezers

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Area of Science:

Genetics
Molecular Biology
Genomic Instability

Background:

Mouse telomeres exhibit characteristics of common fragile sites (CFS), with disrupted signals after aphidicolin treatment.
This fragility is linked to the deletion of TRF1, a shelterin protein crucial for telomere replication.

Purpose of the Study:

To investigate whether chromosome-internal telomeric repeats in humans form aphidicolin-induced CFS.
To determine the role of TRF1 in stabilizing these internal fragile sites.

Main Methods:

Induction of common fragile sites using aphidicolin treatment.
Fluorescent in situ hybridization to analyze telomeric repeat signals.
Analysis of TRF1 binding and its effect on fragile site stability.

Main Results:

Human chromosome 2q14, containing internal TTAGGG repeats, forms an aphidicolin-induced CFS.
TRF1 specifically binds to and stabilizes CFS 2q14.
TRF1 does not influence other common fragile sites, highlighting sequence-specific control.

Conclusions:

Telomeric DNA sequences possess inherent fragility irrespective of their genomic location.
Common fragile sites can arise from specific DNA sequences.
CFS 2q14 is the first identified CFS regulated by a sequence-specific DNA-binding protein, TRF1.