Related Experiment Video
Updated: May 10, 2026
05:37
Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes
Published on: April 4, 2025
Sequence-dependent thymine dimer formation and photoreversal rates in double-stranded DNA
Yu Kay Law1, Robert A Forties, Xin Liu
1Biophysics Program, The Ohio State University, Columbus, OH, USA.
Summary
The formation and reversal of thymine-thymine cyclobutane pyrimidine dimers (TT-CPDs) in DNA are highly sensitive to neighboring base sequences. These DNA damage and repair kinetics are primarily influenced by the bases immediately flanking the photoreactive TT step.
Area of Science:
- Molecular Biology
- Photochemistry
- DNA Damage and Repair
Background:
- Cyclobutane pyrimidine dimers (CPDs) are major DNA lesions induced by UV radiation.
- Thymine-thymine CPDs (TT-CPDs) are the most common type of UV-induced DNA damage.
- Understanding the kinetics of TT-CPD formation and photoreversal is crucial for DNA repair mechanisms.
Purpose of the Study:
- To investigate the site-specific kinetics of TT-CPD formation and photoreversal.
- To determine how the sequence context, specifically nearest-neighbor bases, influences TT-CPD photochemistry.
- To elucidate the role of flanking bases in DNA damage and repair rates.
Main Methods:
- Studied TT-CPD formation at 23 specific TT sites within DNA sequences.
- Utilized site-specific assays with fluorescent labels and T4 pyrimidine dimer glycosylase.
- Employed gel electrophoresis to separate DNA fragments and quantify damage.
- Analyzed kinetic data for both CPD formation and photoreversal reactions.
Main Results:
- TT-CPD yields varied significantly across different tetrads (XTTY), up to an order of magnitude.
- Identical tetrads showed similar TT-CPD yields, indicating sequence specificity.
- Both TT-CPD formation and photoreversal rates were highly dependent on the 5' and 3' flanking bases.
- Purine-purine flanking sequences exhibited the lowest formation and reversal rates.
- Tetrads with at least one flanking cytosine (C) showed the highest formation and reversal rates.
Conclusions:
- Nearest-neighbor base interactions are the principal determinants of TT-CPD formation and photoreversal probabilities.
- The DNA sequence context plays a critical role in modulating UV-induced DNA damage and repair kinetics.
- These findings provide insights into the sequence-dependent susceptibility of DNA to UV damage.
Related Concept Videos
02:31Homologous Recombination
The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
02:04Fixing Double-strand Breaks
The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...
02:10Translesion DNA Polymerases
Translesion (TLS) polymerases rescue stalled DNA polymerases at sites of damaged bases by replacing the replicative polymerase and installing a nucleotide across the damaged site. Doing so, TLS allows additional time for the cell to repair the damage before resuming regular DNA replication.
TLS polymerases are found in all three domains of life - archaea, bacteria, and eukaryotes. Of the different classes of TLS polymerases, members of the Y family are fitted with specialized structures that...
TLS polymerases are found in all three domains of life - archaea, bacteria, and eukaryotes. Of the different classes of TLS polymerases, members of the Y family are fitted with specialized structures that...
01:30Spontaneous and Induced Mutations
Spontaneous mutations arise infrequently during DNA replication due to errors in the process. A key factor behind these errors is tautomeric shifts in nitrogenous bases, where bases transition from keto to enol forms or amino to imino forms. This shift can alter base-pairing rules, leading to mutations. Additionally, reactive oxygen species (ROS) arising from aerobic metabolism can damage DNA, resulting in depurination (loss of a purine base) or depyrimidination (loss of a pyrimidine base).
02:53Conservative Site-specific Recombination and Phase Variation
Because the DNA segments are cut and reorganized in a direction-specific manner, site-specific recombination has emerged as an efficient genetic engineering technique. Flippase and Cyclization recombinases or Flp and Cre, respectively, are two members of the tyrosine recombinase family derived from bacteriophages, that are used to mediate site-specific DNA insertions, deletions, and targeted expression of proteins in mammalian cell lines.
The recognition sites for Cre recombinase called LoxP...
The recognition sites for Cre recombinase called LoxP...
02:02DNA Topoisomerases
Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
Types and Mechanism of action
Topoisomerases are divided into two main types. Type I...
Types and Mechanism of action
Topoisomerases are divided into two main types. Type I...