| Abstract: | SV40 and pBR322 DNAs damaged by ultraviolet light were cleaved abnormally by several restriction enzymes because of damage to pyrimidines in the recognition sequences. The use of a tandemly duplicated plasmid provided a particularly sensitive target molecule for detecting pyrimidine dimers and other possible photoproducts. The relative efficiency with which cleavage was blocked (HindIII greater than TaqI greater than EcoRI greater than BamI greater than SalI much greater than Hha I, Hae III) corresponds approximately to the relative frequency of pyrimidine dimer formation in the recognition sequences, but at a slightly higher frequency in potential sites for the non-cyclobutane T-C product. The pyrimidine dimers appear to have a range of influence that extends 1 to 3 basepairs along the DNA molecule. These effects provide clues to the way DNA damage from mutagens and carcinogens can interfere with specific enzyme-DNA interactions. |
