1. Cell Cycle Group, MRC Clinical Sciences Centre, Imperial College, Du Cane Road, London W12 0NN, UK
2. Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, 442 Kaul Human Genetics Building, 720 20th Street South, Birmingham, Alabama 35294, USA
3. Institut für Biochemie, Mikrobiologie und Genetik, Universität Regensburg, Munich, Germany
4. Present address: Unidad de Investigación, Hospital Universitario Candelaria, Carretera del Rosario, 38010 Tenerife, Spain.

Correspondence to: Luis Aragón¹ Correspondence and requests for materials should be addressed to L.A. (Email: luis.aragon@csc.mrc.ac.uk).

Abstract

Chromosome condensation and the global repression of gene transcription¹ are features of mitosis in most eukaryotes. The logic behind this phenomenon is that chromosome condensation prevents the activity of RNA polymerases. In budding yeast, however, transcription was proposed to be continuous during mitosis². Here we show that Cdc14, a protein phosphatase required for nucleolar segregation³ and mitotic exit⁴, inhibits transcription of yeast ribosomal genes (rDNA) during anaphase. The phosphatase activity of Cdc14 is required for RNA polymerase I (Pol I) inhibition in vitro and in vivo. Moreover Cdc14-dependent inhibition involves nucleolar exclusion of Pol I subunits. We demonstrate that transcription inhibition is necessary for complete chromosome disjunction, because ribosomal RNA (rRNA) transcripts block condensin binding to rDNA, and show that bypassing the role of Cdc14 in nucleolar segregation requires in vivo degradation of nascent transcripts. Our results show that transcription interferes with chromosome condensation, not the reverse. We conclude that budding yeast, like most eukaryotes, inhibit Pol I transcription before segregation as a prerequisite for chromosome condensation and faithful genome separation.

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