Pyrimidine dimers induced in Escherichia coli DNA by ultraviolet radiation present in sunlight.

Escherichia coli DNA was irradiated with various wavelengths of monochromatic UV light from 254 to 320 nm, and the relative yields of the different cyclobutane pyrimidine dimers determined. Cytosine-thymine dimers (C mean value of T) were more frequent than thymine dimers (T mean value of T) at low fluences of 300 and 313 nm light, whereas the reverse was true at either longer or shorter wavelengths. Thus, in the solar UV range deemed responsible for skin cancer (i.e. 295-315 nm), C mean value of T are probably more important than T mean value of T.