Repair in E. coli of transforming plasmid DNA damaged by psoralen plus near-ultraviolet irradiation

Treatment of DNA with psoralen plus near-ultraviolet irradiation gives rise to both monoadducts and cross-links. The authors have examined the repair of plasmid NTP16 DNA treated in this way in vitro and then used to transform E. coli. Monoadducts are found to be potentially lethal, and can be repaired by uvr-dependent and recA-dependent pathways. The presence of a related resident plasmid in the transformed cells can enhance the survival of the incoming damaged NTP16 DNA. This effect is not recA-dependent. Removal of unbound psoralen from the plasmid DNA and exposure to further NUV is known to increase the ratio of cross-links to monoadducts, and the authors demonstrate that such cross-linked plasmid DNA is not readily repaired following transformation. However in the presence of homologous DNA there is evidence for the repair, and hence uptake by the cell, of cross-linked DNA. (Auth.)