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Position-effect Variegation

Position-effect Variegation

In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.

Inheritance of Chromatin Structures

Inheritance of Chromatin Structures

Epigenetics is the study of inherited changes in a cell's phenotype without changing the DNA sequences. It provides a form of memory for the differential gene expression pattern to maintain cell lineage, position-effect variegation, dosage compensation, and maintenance of chromatin structures such as telomeres and centromeres. For example, the structure and location of the centromere on chromosomes are epigenetically inherited. Its functionality is not dictated or ensured by the underlying DNA...

DNA-only Transposons

DNA-only Transposons

DNA-only transposons are called autonomous transposons since they code for the enzyme transposase that is required for the transposition mechanism. Insertion of transposons can alter gene functions in multiple ways. They can mutate the gene, alter gene expression by introducing a novel promoter or insulator sequence, introduce new splice sites, and change the mRNA transcripts produced, or remodel chromatin structure.
The donor site from where the transposon is excised is either degraded or...

Heterochromatin

Heterochromatin

The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions that take up more dye are called heterochromatin. Heterochromatin is further classified into two forms – constitutive heterochromatin and facultative heterochromatin.
Constitutive heterochromatin: It is a highly compact region of chromatin that is mostly concentrated in the centromere and telomere. Unlike euchromatin, the amino acid at 9th...

Heterochromatin

Heterochromatin

The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions that take up more dye are called heterochromatin. Heterochromatin is further classified into two forms – constitutive heterochromatin and facultative heterochromatin.
Constitutive heterochromatin: It is a highly compact region of chromatin that is mostly concentrated in the centromere and telomere. Unlike euchromatin, the amino acid at 9th...

X-Inactivation

X-Inactivation

The human X chromosome contains over ten times the number of genes as in the Y chromosome. Since males have only one X chromosome, and females have two, one might expect females to produce twice as many of the proteins, with undesirable results.

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Updated: Jul 8, 2026

Plasmid-derived DNA Strand Displacement Gates for Implementing Chemical Reaction Networks

Plasmid-derived DNA Strand Displacement Gates for Implementing Chemical Reaction Networks

Published on: November 25, 2015

Intercalation is not required for DNA light-switch behavior.

Daniel A Lutterman¹, Abdellatif Chouai, Yao Liu

¹Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA.

Journal of the American Chemical Society

|January 9, 2008

Summary

This summary is machine-generated.

This study reveals that a bimetallic ruthenium complex acts as a DNA light-switch without intercalating into DNA. This finding challenges the assumption that light-switch behavior exclusively confirms DNA intercalation.

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Plasmid-derived DNA Strand Displacement Gates for Implementing Chemical Reaction Networks

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DNA-Tethered RNA Polymerase for Programmable In vitro Transcription and Molecular Computation

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Published on: December 29, 2021

Area of Science:

Coordination Chemistry
Bioinorganic Chemistry
Photochemistry

Background:

Transition metal complexes exhibiting luminescence upon DNA binding are often assumed to intercalate.
The DNA light-switch complex [Ru(bpy)2(tpphz)]2+ (1) is emissive when bound to DNA.

Purpose of the Study:

To investigate the DNA binding and luminescent properties of the nonintercalating bimetallic complex [(bpy)2Ru(tpphz)Ru(bpy)2]4+ (2).
To determine if light-switch behavior can occur without DNA intercalation.

Main Methods:

Spectroscopic analysis (emission spectroscopy) of complex 2 in the presence of calf thymus DNA (ct-DNA) and herring sperm DNA.
Viscosity measurements to assess DNA intercalation.
Density Functional Theory (DFT) calculations to understand electronic properties.

Main Results:

Complex 2 exhibits a 40-fold increase in luminescence intensity with a red shift upon binding to ct-DNA.
Viscosity measurements and threading experiments confirm that complex 2 does not intercalate into DNA.
DFT calculations support the observed luminescence properties, correlating them with electronic structure.

Conclusions:

The bimetallic complex 2 functions as a DNA light-switch through a nonintercalating mechanism.
This work presents the first example of a nonintercalating metal complex demonstrating light-switch behavior.
Light-switch behavior is not exclusively indicative of DNA intercalation.