Photolyases from Saccharomyces cerevisiae and Escherichia coli recognize common binding determinants in DNA containing pyrimidine dimers.

Abstract

DNA photolyases catalyze the light-dependent repair of pyrimidine dimers in DNA. The results of nucleotide sequence analysis and spectroscopic studies demonstrated that photolyases from Saccharomyces cerevisiae and Escherichia coli share 37% amino acid sequence homology and contain identical chromophores. Do the similarities between these two enzymes extend to their interactions with DNA containing pyrimidine dimers, or does the organization of DNA into nucleosomes in S. cerevisiae necessitate alternative or additional recognition determinants? To answer this question, we used chemical and enzymatic techniques to identify the contacts made on DNA by S. cerevisiae photolyase when it is bound to a pyrimidine dimer and compared these contacts with those made by E. coli photolyase and by a truncated derivative of the yeast enzyme when bound to the same substrate. We found evidence for a common set of interactions between the photolyases and specific phosphates in the backbones of both strands as well as for interactions with bases in both the major and minor grooves of dimer-containing DNA. Superimposed on this common pattern were significant differences in the contributions of specific contacts to the overall binding energy, in the interactions of the enzymes with groups on the complementary strand, and in the extent to which other DNA-binding proteins were excluded from the region around the dimer. These results provide strong evidence both for a conserved dimer-binding motif and for the evolution of new interactions that permit photolyases to also act as accessory proteins in nucleotide excision repair. The locations of the specific contacts made by the yeast enzyme indicate that the mechanism of nucleotide excision repair in this organism involves incision(s) at a distance from the pyrimidine dimer.