Photoproduct SAR

DNA Photoproduct Structure-Activity Relationships in Skin Cancer Induction. Though many of the carcinogenic effects of sunlight can be attributed to DNA photo-products, such as the cis-syn dimer, the biological activities of individual photoproducts are largely unknown. To determine the precise structure activity relationships of DNA photoproducts, we have been pursing combined physical, synthetic organic, and biological studies of these photoproducts and their interactions with transcription factors, repair enzymes and DNA and RNA polymerases both in vitro and in vivo. Our approach rests on the preparation DNA containing site-specific photoproducts (Figure 2) that is prepared by either the direct irradiation of short oligodeoxynucleotides (ODNs) or on the synthesis of building blocks for the site-specific incorporation of DNA photoproducts photoproducts into ODNs by automated synthesis.

We have succeeded in preparing a wide variety of photoproduct-containing substrates that have been implicated in substitution and frameshift mutations. All of these photoproducts result from an initial [2+2] photoreaction which may be followed by subsequent thermal or photochemical reactions.

Our main focus has been on understanding the mechanism of C to T and CC to TT mutations, and have been focusing on understanding the structure-activity relationships in deamination of C within cis-syn cyclobutane dimers and have recently completed a study of the sequence dependence of deamination. Currently, we are investigating the effect of protein binding and nucleosome structure on deamination.

Recently we discovered the formation of an unexpected anti-thymine dimer photoproduct when irradiating a single-stranded 14-mer ODN which must have arisen from an as yet unknown folded structure. This led us to investigate the photochemistry of human telomere DNA (the DNA at the ends of chromosomes) which adopts highly unusual G-quadruplex structures in vitro. Not unexpectedly, irradiation of a short fragment of the human telomeric DNA resulted in photocrosslinking between two of the loops. This could have implications for the effects of sunlight on DNA replication.

We have also been investigating the effect of nucleosome structure on DNA photoproduct formation and deamination and the effect of photoproducts on the dyanmics of the nucleosome, both in vitro and in vivo.