Differential roles of phosphorylation in the formation of transcriptional active RNA polymerase I

doi:10.1073/pnas.231181398

Differential roles of phosphorylation in the formation of transcriptional active RNA polymerase I

^*Biochemie-Zentrum Heidelberg, Im Neuenheimer Feld 328, D-69120 Heidelberg, Germany; and ^‡Service de Biochimie et de Génétique Moléculaire, Commissariat à l'Energie Atomique/Saclay, F-91191 Gif sur Yvette Cedex, France

Edited by Roger D. Kornberg, Stanford University School of Medicine, Stanford, CA, and approved August 24, 2001 (received for review April 11, 2001)

Abstract

Regulation of rDNA transcription depends on the formation and dissociation of a functional complex between RNA polymerase I (pol I) and transcription initiation factor Rrn3p. We analyzed whether phosphorylation is involved in this molecular switch. Rrn3p is a phosphoprotein that is predominantly phosphorylated in vivo when it is not bound to pol I. In vitro, Rrn3p is able both to associate with pol I and to enter the transcription cycle in its nonphosphorylated form. By contrast, phosphorylation of pol I is required to form a stable pol I-Rrn3p complex for efficient transcription initiation. Furthermore, association of pol I with Rrn3p correlates with a change in the phosphorylation state of pol I in vivo. We suggest that phosphorylation at specific sites of pol I is a prerequisite for proper transcription initiation and that phosphorylation/dephosphorylation of pol I is one possibility to modulate cellular rDNA transcription activity.

Footnotes

↵ † Present address: Centre National de la Recherche Scientifique-Laboratoire Moléculaire Biologie Eucaryote 118, Route de Narbonne, F-31062 Toulouse, France.
↵ § To whom reprint requests should be addressed at: Institute für Biochemie, Universtät Heidelberg, Im Neuenheimer Feld 328, D-69120 Heidelberg, Germany. E-mail: im4{at}popix.urz.uni-heidelberg.de.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

pol I,

RNA polymerase I;

ProtA,

ProteinA-epitope;

HA,

hemagglutinin antigen;

UAF,

upstream activating factor;

CF,

core factor;

TBP,

TATA binding protein;

AMP-PNP,

adenosine 5′-[β,γ-imido]triphosphate