Direct demonstration of the monomerization of thymine-containing dimers in U.V.-irradiated DNA by yeast photoreactivating enzyme and light

Abstract— Ultraviolet-irradiated E. coli DNA (³H-thymine-labelled) was mixed with un-irradiated E. coli DNA (¹⁴C-thymine-labelled) and exposed to light in the presence of purified yeast photoreactivating enzyme. As the ³H-thymine-containing cyclobutane dimers disappeared during the photoreactivation, there was a stoichiometric increase of monomeric ³H-thymine as determined from the ³H/¹⁴C ratio in thymine. This is the first direct demonstration that thymine-containing dimers in u.v.-irradiated DNA are monomerized by yeast photoreactivating enzyme in the presence of light.