Identification of two steps during Xenopus ribosomal gene transcription that are sensitive to protein phosphorylation.
Protein kinase(s) and protein phosphatase(s) present in a Xenopus S-100 transcription extract strongly influence promoter-dependent transcription by RNA polymerase I. The protein kinase inhibitor 6-dimethyl-aminopurine causes transcription to increase, while the protein phosphatase inhibitor okadaic acid causes transcription to decrease. Repression is also observed with inhibitor 2, and the addition of extra protein phosphatase 1 stimulates transcription, indicating that the endogenous phosphatase is a type 1 enzyme. Partial fractionation of the system, single-round transcription reactions, and kinetic experiments show that two different steps during ribosomal gene transcription are sensitive to protein phosphorylation: okadaic acid affects a step before or during transcription initiation, while 6-dimethylaminopurine stimulates a process "late" in the reaction, possibly reinitiation. The present results are a clear demonstration that transcription by RNA polymerase I can be regulated by protein phosphorylation.
Labhart
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Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, California 92037.
D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002474:Cell-Free System; D004275:DNA, Ribosomal / Q000235:genetics*; D004988:Ethers, Cyclic / Q000494:pharmacology; D005786:Gene Expression Regulation; D066298:In Vitro Techniques; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010750:Phosphoproteins / Q000502:physiology*; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D054645:Protein Phosphatase 1; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D014158:Transcription, Genetic; D014982:Xenopus laevis / Q000235:genetics*
D004275:DNA, Ribosomal; D004988:Ethers, Cyclic; D010750:Phosphoproteins; D047428:Protein Kinase Inhibitors; D012335:RNA, Ribosomal; D019319:Okadaic Acid; C001020:N(6),N(6)-dimethyladenine; D011494:Protein Kinases; D012318:RNA Polymerase I; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D000225:Adenine