Two DNA endonuclease activities from normal human and xeroderma pigmentosum chromatin active on psoralen plus ultraviolet light treated DNA

DNA endonuclease activities from the chromatin of normal human and xeroderma pigmentosum, complementation group A (XPA), lymphoblastoid cells were examined on DNA treated with 8-methoxypsoralen (8-MOP) or 4,5',8-trimethylpsoralen (TMP) plus long wavelength ultraviolet (UVA) light, which produce monoadducts and DNA interstrand cross-links, and angelicin plus UVA light, which produces mainly monoadducts. 9 chromatin-associated DNA endonuclease activities were isolated from normal and XPA cells and assayed for activity on PM2 bacteriophage DNA that had been treated with 8-MOP or TMP in the dark and then exposed to UVA light. Unbound psoralen was removed by dialysis and a second dose of UVA light was given. The results indicate that in both normal and XPA cells there are at least two different DNA endonucleases which act on both 8-MOP and TMP plus UVA light treated DNA. 40 refs.; 2 figs.; 1 table