Regulation of 2',5'-oligo(A) synthetase activity in theophylline-treated NIH 3T3 cells

Sequential treatment of NIH 3T3 cells with theophylline and actinomycin D results in an enhancement of 2',5'-oligo(A) synthetase activity 2-3-fold exceeding that induced by treatment with theophylline only. This 'superinduction' phenomenon suggests the existence of a negative control of the enzyme that involves a labile, transcription-dependent factor.