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Abstract:
Approximately 90 min after the application of dexamethasone, an increase in the activity of the liver enzymes tryptophan oxygenase and tyrosine aminotransferase in adrenalectomized male rats could be measured. As early as 30 sec after the injection of an inducing amount of [3H]dexamethasone, significant radioactivity can be found in purified rat liver nuclei. The uptake is linear during the first 15 min, whereas during the same time period, the increase of the radioactivity in the 10,000g supernatant is biphasic. No time shift could be observed in the uptake of dexamethasone by nuclei as compared to the accumulation in the 10,000g supernatant. Studies on the time course of sensitivity of the induction process to α-amanitin suggested that the first induced transcripts for tryptophan oxygenase and tyrosine aminotransferase are completed about 25 min after the administration of the hormone. The ensuing processing of the transcripts to the corresponding mRNAs can be blocked by actinomycin D, the actinomycin D-sensitive phase lasting another 15–25 min. A lag phase of approximately 20 min has been calculated from the time of the entry of the first hormone molecules into the nucleus till the initiation of specific tryptophan oxygenase and tyrosine aminotransferase gene transcription.
