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Casein Kinase 2 Associates with Initiation-Competent RNA Polymerase I and Has Multiple Roles in Ribosomal DNA Transcription

Tatiana B. Panova, Kostya I. Panov, Jackie Russell, and Joost C. B. M. Zomerdijk^*

Division of Gene Regulation and Expression, Wellcome Trust Biocentre, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom

Received 18 April 2006/ Returned for modification 9 May 2006/ Accepted 1 June 2006

Mammalian RNA polymerase I (Pol I) complexes contain a number of associated factors, some with undefined regulatory roles in transcription. We demonstrate that casein kinase 2 (CK2) in human cells is associated specifically only with the initiation-competent Pol Iß isoform and not with Pol I. Chromatin immunoprecipitation analysis places CK2 at the ribosomal DNA (rDNA) promoter in vivo. Pol Iß-associated CK2 can phosphorylate topoisomerase II in Pol Iß, activator upstream binding factor (UBF), and selectivity factor 1 (SL1) subunit TAF_I110. A potent and selective CK2 inhibitor, 3,8-dibromo-7-hydroxy-4-methylchromen-2-one, limits in vitro transcription to a single round, suggesting a role for CK2 in reinitiation. Phosphorylation of UBF by CK2 increases SL1-dependent stabilization of UBF at the rDNA promoter, providing a molecular mechanism for the stimulatory effect of CK2 on UBF activation of transcription. These positive effects of CK2 in Pol I transcription contrast to that wrought by CK2 phosphorylation of TAF_I110, which prevents SL1 binding to rDNA, thereby abrogating the ability of SL1 to nucleate preinitiation complex (PIC) formation. Thus, CK2 has the potential to regulate Pol I transcription at multiple levels, in PIC formation, activation, and reinitiation of transcription.

These authors contributed equally to this work.