Block of cleavage of ultraviolet-irradiated DNA with restriction endonucleases.

pBR322/Ultraviolet irradiation/Restriction endonuclease/Pyrimidine dimer Plasmid pBR322 DNA was irradiated with ultraviolet light at 254 nm and digested with various restric tion endonucleases. Analyses of the products suggested that the pyrimidine dimers which would have been formed just across the cutting site (Acc I), at the opposite position of the cutting site (Hind III, Eco RI, Bam HI), and at the position adjacent to the cutting site (Aha III) blocked the cleavage with the enzymes. In addition, experiments with Hind III, Eco RI and Bam HI showed that the extent of cleavage block appears to reflect the relative efficiency of dimer formation in sequences, TT, CT and CC.