Expression Of Frog Virus-3 Early Genes After Ultraviolet-Irradiation

The synthesis of early gene products was studied in Chinese hamster ovary (CHO) cells infected with FV 3 virions irradiated with various doses of uv light. The transcription of the immediate early units, occurring in the presence of cycloheximide, was analyzed by quantitation of the polypeptides synthesized after drug removal, pulse labeled with [ 35 S]methionine, and separated by gel electrophoresis. A distinct inactivation rate of protein synthesis was observed for four immediate early species (54K, 42K, 20K, 16K) and the uv target sizes were found to be proportional to the molecular weight of the encoded polypeptides. Delayed early species were analyzed in the absence of genome replication. Under these conditions the delayed early genes (coding for polypeptides 90K and 31K) and the gene for one immediate early species 16K showed target sizes greater than that of polypeptide 42K. The results suggest that the immediate early mRNA species whose translation was detectable in vivo are transcribed from individual promoter regions; they also reflect the fact that the expression of the gene coding for polypeptide 42K is controlled by at least one of the early products and/or the dependence of early genes upon the immediate early protein 42K.