Early events in the stimulation of mammary tumor virus RNA synthesis by glucocorticoids. Novel assays of transcription rates

Two procedures were devised to examine initial events in the glucocorticoid-regulated transcription of integrated murine mammary tumor virus (MTV) DNA sequences. First, cells in monolayer culture were exposed for brief periods to dexamethasone and then permeabilized in situ with digitonin to allow e...

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Bibliographic Details
Published in:The Journal of biological chemistry 1984-06, Vol.259 (12), p.7416-7420
Main Authors: Ucker, D S, Yamamoto, K R
Format: Article
Language:English
Subjects:
Animals
Base Sequence
Biological and medical sciences
Dexamethasone - pharmacology
Digitonin - pharmacology
Endonucleases - metabolism
Fundamental and applied biological sciences. Psychology
Gene expression
Mammary Tumor Virus, Mouse - genetics
Molecular and cellular biology
Molecular genetics
Nucleic Acid Hybridization
Rats
RNA, Viral - biosynthesis
Single-Strand Specific DNA and RNA Endonucleases
Time Factors
Transcription, Genetic - drug effects
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Summary:Two procedures were devised to examine initial events in the glucocorticoid-regulated transcription of integrated murine mammary tumor virus (MTV) DNA sequences. First, cells in monolayer culture were exposed for brief periods to dexamethasone and then permeabilized in situ with digitonin to allow entry of 32P-labeled ribonucleoside triphosphates and measurement of transcription rates. The results revealed that the rate of MTV RNA synthesis is stimulated selectively by dexamethasone after an apparent lag of approximately equal to 1 min and is half-maximal by 8-9 min. Second, the time course of transcription elongation was monitored by quantitating in single strand nuclease protection assays the accumulation of RNA sequences from different regions of the 7.8-kilobase MTV transcription unit. These experiments suggested that the rate of MTV RNA elongation in the presence of hormone does not differ substantially from elongation rates calculated for other genes transcribed by RNA polymerase II. Moreover, dexamethasone increased in parallel and to the same extent the levels of RNA from various segments of the transcription unit, implying that transcripts are elongated across the MTV element at a constant rate. We conclude that glucocorticoids stimulate MTV transcription solely via a rapid and selective increase in the efficiency of transcription initiation.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(17)42806-7