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Molecular and Cellular Biology, October 2001, p. 6359-6368, Vol. 21, No. 19
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.19.6359-6368.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Transcription-Independent RNA Polymerase II Dephosphorylation by the FCP1 Carboxy-Terminal Domain Phosphatase in Xenopus laevis Early Embryos

Benoît Palancade,1 Marie Françoise Dubois,1 Michael E. Dahmus,2 and Olivier Bensaude1,*

Génétique Moléculaire, UMR 8541 CNRS, Ecole Normale Supérieure, 75230 Paris Cedex 05, France,1 and Section of Molecular and Cellular Biology, University of California, Davis, California 956162

Received 8 May 2001/Returned for modification 4 June 2001/Accepted 20 June 2001

The phosphorylation of the RNA polymerase II (RNAP II) carboxy-terminal domain (CTD) plays a key role in mRNA metabolism. The relative ratio of hyperphosphorylated RNAP II to hypophosphorylated RNAP II is determined by a dynamic equilibrium between CTD kinases and CTD phosphatase(s). The CTD is heavily phosphorylated in meiotic Xenopus laevis oocytes. In this report we show that the CTD undergoes fast and massive dephosphorylation upon fertilization. A cDNA was cloned and shown to code for a full-length xFCP1, the Xenopus orthologue of the FCP1 CTD phosphatases in humans and Saccharomyces cerevisiae. Two critical residues in the catalytic site were identified. CTD phosphatase activity was observed in extracts prepared from Xenopus eggs and cells and was shown to be entirely attributable to xFCP1. The CTD dephosphorylation triggered by fertilization was reproduced upon calcium activation of cytostatic factor-arrested egg extracts. Using immunodepleted extracts, we showed that this dephosphorylation is due to xFCP1. Although transcription does not occur at this stage, phosphorylation appears as a highly dynamic process involving the antagonist action of Xp42 mitogen-activated protein kinase and FCP1 phosphatase. This is the first report that free RNAP II is a substrate for FCP1 in vivo, independent from a transcription cycle.

* Corresponding author. Mailing address: Génétique Moléculaire, UMR 8541 CNRS, Ecole Normale Supérieure, 46 rue d'Ulm, 75230 Paris Cedex 05, France. Phone: 33 1 44 32 34 10. Fax: 33 1 44 32 39 41. E-mail: bensaude{at}ens.fr.

Molecular and Cellular Biology, October 2001, p. 6359-6368, Vol. 21, No. 19
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.19.6359-6368.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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