Inhibition of messenger RNA accumulation but not translation in ultraviolet irradiated hepatoma cells

Irradiation by ultraviolet light at doses between 30 and 90 ergs/mm² increasingly inhibited the hydrocortisone but not the insulin induction of tyrosine aminotransferase activity in Reuber (H35) hepatoma cells in culture. Incorporation of lecuine into cellular protein was only slightly inhibited in this dose range. Incorporation of uridine into RNA in the presence of low doses of actinomycin D (0.1 μg/ml) was increasingly inhibited by ultraviolet irradiation. Since cellular uptake of uridine into the acid soluble pool was not inhibited by ultraviolet irradiation, the inhibition of RNA labeling suggests inhibition of synthesis of heterogenous nuclear RNA by low doses of ultraviolet irradiation. "Unscheduled" DNA synthesis was initially stimulated 2 fold by 30 ergs/mm² irradiation and returned to control levels in 8 hours. Thus, ultraviolet irradiation in the low dose range causes DNA repair synthesis, inhibits transcription and apparently tyrosine aminotransferase messenger RNA accumulation while pre-existing cytoplasmic messenger appears not to be inactivated nor its translation inhibited.