UV INDUCED (6‐4) PHOTOPRODUCTS ARE DISTRIBUTED DIFFERENTLY THAN CYCLOBUTANE DIMERS IN NUCLEOSOMES

Abstract
Abstract— We have compared the distributions of two stable UV photoproducts in nucleosome core DNA at the single‐nucleotide level using a T4 polymerase‐exonuclease mapping procedure. The distribution of pyrimidine‐pyrimidone (6‐4) dimers was uncovered by reversing the major UV photo‐product, cis‐syn cyclobutane pyrimidine dimer, with E. coli DNA photolyase and photoreactivating light. Whereas the distribution of total UV photoproducts in nucleosome core DNA forms a striking 10.3 base periodic pattern, the distribution of (6‐4) dimers is much more random throughout the nucleosome core domain. Therefore, histone‐DNA interactions in nucleosomes strongly modulate formation of the major class of UV‐induced photoproducts, while having either a constant effect or no effect on (6‐4) dimer formation.