Effects of inhibitors of DNA synthesis and protein synthesis on the rate of DNA synthesis after exposure of mammalian cells to ultraviolet light

Chinese hamster V-79 cells were treated with metabolic inhibitors of DNA or protein synthesis for various intervals of time after exposure of 3.0 or 5.0 J · m⁻². After removal of the metabolic block(s) the rate of DNA synthesis was followed by measuring the incorporation of [¹⁴C]thymidine into acid-insoluble material. A 2.5 or 5.0 h incubation with cycloheximide or hydroxyurea was effective in delaying the onset of the recovery in the rate of DNA synthesis that normally becomes evident several hours after exposure to ultraviolet light. By using concentrations of cycloheximide or hydroxyurea that inhibit DNA synthesis by a similar amount (70%), but protein synthesis by vastly different amounts (95% for cycloheximide; 0% for hydroxyurea), it was apparent that the delay in recovery caused by the treatment of the cells with cycloheximide could be accounted for entirely by its inhibitory effect on DNA synthesis. This suggests that the recovery in DNA synthetic rates following exposure of V-79 cells to ultraviolet light does not appear to require de novo protein synthesis, and therefore does not appear to require the involement of an inducible DNA repair process.