CU(II) SENSITIZES PBR322 PLASMID DNA TO INACTIVATION BY UV-B (280-315-NM)

Copper(II), in the presence of UV-B radiation (280-315 nm), can genera te single-strand breaks in the sugar-phosphate backbone of pBR322 plas mid DNA. A low level of single-strand backbone breaks occurs in the pr esence of Cu(II) alone, but UV-B irradiation increases the rate by the more than 100-fold. Concomitant with the damage to the DNA backbone i s a loss of transforming activity. Oxygen is required for generation o f the single-strand breaks but not for the loss of transforming activi ty. A DNA glycosylase (Fpg), which participates in the repair of certa in DNA nitrogenous base damage, does not repair plasmid DNA damaged by Cu(II). The hydroxyl radical scavenging compound DMSO is only somewha t effective at protecting the physical and biological properties of th e DNA. These results with Cu(II) are compared to those obtained previo usly with pBR322 plasmid DNA in the presence of Fe(III) and UV-A.