UVB and UVA radiation-mediated damage to isolated and cellular DNA

Abstract

Abstract:The effects of solar light on cellular DNA are mostly explained by both direct excitation of nucleobases and photosensitized reactions that are mediated by UVB and UVA radiation, respectively. A large body of information is now available on the main photodynamic reactions to DNA, which involve guanine as the preferential target of both one-electron oxidation and singlet oxygen oxidation, as the result of type I and type II mechanisms. Most of the final products of the photosensitized reactions of guanine base in isolated DNA have been characterized, and comprehensive mechanisms for their formation have been proposed. Further insights into the mechanisms of solar radiation-induced modifications within cellular DNA have been gained from accurate measurement of the main photoproducts using recently designed sensitive chromatographic and biochemical methods. Thus, the distribution pattern of the 12 possible bipyrimidine photoproducts has been shown to be similar in the DNA of UVB-irradiated rodent and human cells. Cyclobutyl pyrimidine dimers are also generated at di-thymine and thymine-cytosine sites within nuclear DNA upon exposure to UVA radiation as the likely result of triplet energy transfer. In addition, oxidative reactions that involved mostly singlet oxygen, and to a lesser extent, ؒ OH radicals are also implicated, although less efficiently.

Site‐Selective Blocking of PCR by a Caged Nucleotide Leading to Direct Creation of Desired Sticky Ends in The Products

“…Firstly, recognition sites of type II restriction enzymes, which are most often used in these fields, are mostly limited to certain palindromic sequences, and it is sometimes difficult to find an appropriate enzyme to digest DNA at (or near) the target manipulation site. Secondly, most of these A C H T U N G T R E N N U N G enzymes recognize only four to eight DNA base sequences, so precise manipulation of large vectors such as adenovirus (30)(31)(32)(33)(34)(35)(36)(37)(38) kbp) with restriction enzymes is not very practical because digestion occurs at too many sites in such large DNA sequences.…”

Ultrafast IR spectroscopy of the short-lived transients formed by UV excitation of cytosine derivatives

“…1 The nucleobases fluoresce extremely weakly and this has led to the conclusion that their excited states must be very short-lived. 2 This is supported by femtosecond transient visible absorption 3 and fluorescence upconversion 4 measurements that reveal that the bases and mononucleotides possess sub-picosecond excited state lifetimes.…”

Picosecond Transient Infrared Study of the Ultrafast Deactivation Processes of Electronically Excited B‐DNA and Z‐DNA Forms of [poly(dG‐dC)]2

“…[1] Considerable effort has focused on the photophysics and photochemistry of the individual base components which have very short electronically excited singlet state lifetimes (< 1 ps). However, such studies are essential for the understanding of the nature and dynamics of the UV-activated processes that precede DNA damage and lead to mutagenesis and ultimately cause a number of diseases.…”