Sites of preferred interaction between double-stranded pBR322 DNA and 7-methylpyrido[3,4-c]psoralen

7-Methylpyrido[3,4-c]psoralen has recently been found to photosensitize the crosslinking and cleavage of double-stranded pBR322 DNA (4361 bp) with an unusual degree of site specificity. Following cleavage of the photosensitized pBR322 with the restriction enzymes Pvu II and BamH I, the main fragments were analyzed electrophoretically. Only three possible cleavage areas on the plasmid were suggested by this analysis. They were within the ranges bounded by the positions 801-926, 3172-3303 and 4226-4310. The sensitizer also induced selective cleavage in the related plasmid pUC19 (2686 bp), but the pattern was somewhat more complicated and was not analyzed in detail.