Crosslinking and cleavage of pBR322 DNA photosensitized by 7-methylpyrido[3,4-c]psoralen.

7-Methylpyrido[3,4-c]psoralen (7-MPP) had been designed to be a monofunctional sensitizer in which the pyrone double bond, being engaged in a pyridine ring, would be incapable of participating in the formation of a cyclobutane ring with a DNA component. However, one example of photosensitization of thymine-thymine dimer formation in DNA by 7-MPP had been reported. This paper proves that 7-MPP can sensitize interstrand crosslinks in pBR322 DNA. It also proves that 7-MPP photosensitizes double strand cleavage reactions in the DNA with an unusually large degree of site selectivity.