Pyrimidine dimers: effect of temperature on photoinduction.

Ultraviolet-induced pyrimidine dimer formation in DNA and polyuridylic acid was inhibited on irradiation at 77 degrees K. Enhancement of thymine dimer formation in solutions of DNA occurred upon addition of ethylene glycol. Low temperature measurements of absorbance of polyuridylic acid at low temperature showed that no significant alteration of the residues occurred after irradiation at 77 degrees K and before thawing.