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Thymine dissociation and dimer formation: A Raman and synchronous fluorescence spectroscopic study
Anushka Nagpal1, Dinesh Dhankhar1, Thomas C Cesario2
1Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843.
Summary
Ultraviolet (UV) light causes thymine dimer formation, a DNA damage that inhibits replication. Raman spectroscopy revealed an equilibrium limiting dimer formation, while mutagenic photoproducts continued to increase with UV exposure.
Area of Science:
- Photochemistry
- Molecular Spectroscopy
- Biophysics
Background:
- DNA damage from ultraviolet (UV) radiation is a critical factor in cellular inactivation.
- Thymine dimers and (6-4) photoproducts are major UV-induced DNA lesions.
- Understanding the kinetics of photoproduct formation is essential for comprehending DNA repair and mutagenesis.
Purpose of the Study:
- To investigate the formation of thymine dimers and mutagenic (6-4) photoproducts in thymine solutions and DNA upon UV irradiation.
- To determine the mechanism and kinetics of thymine dimer formation using spectroscopic methods.
- To correlate DNA damage with potential bacterial inactivation.
Main Methods:
- Absorption, fluorescence, synchronous fluorescence, and Raman spectroscopy were employed.
- Spectra of nonirradiated and UV-irradiated thymine solutions and calf thymus DNA were analyzed.
- Raman spectroscopy quantified thymine dimer formation as a function of UV irradiation dose.
Main Results:
- Raman spectroscopy confirmed thymine dimer formation in both solutions and DNA.
- Synchronous fluorescence identified the formation of the mutagenic (6-4) photoproduct.
- Thymine dimer formation rate decreased after 20 min of UV irradiation due to equilibrium.
- The (6-4) photoproduct formation increased with continued UV irradiation.
Conclusions:
- Spectroscopic data elucidate the mechanism of thymine dimer formation.
- An equilibrium between thymine dimers and monomers limits dimer accumulation.
- The (6-4) photoproduct continues to form, contributing to DNA damage.
- Thymine dimer formation is linked to DNA replication inhibition and bacterial inactivation.
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