MCB Accepts, published online ahead of print on 2 September 2008

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Mol. Cell. Biol. doi:10.1128/MCB.00703-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Transcription of Multiple Yeast rDNA Genes Requires Targeting of UAF to the Promoter by Uaf30

Robert D. Hontz, Sarah L. French, Melanie L. Oakes, Prasad Tongaonkar, Masayasu Nomura, Ann L. Beyer, and Jeffrey S. Smith^*

Department of Biochemistry and Molecular Genetics, Department of Microbiology, University of Virginia Health System, School of Medicine, Charlottesville, VA 22908; Department of Biological Chemistry, Department of Pathology and Laboratory of Medicine, University of California, Irvine, Irvine, CA 92697

^* To whom correspondence should be addressed. Email: jss5y{at}virginia.edu.

UAF is a multi-subunit complex that functions in the activation of rDNA transcription by RNA polymerase I (Pol I). Cells lacking the Uaf30 subunit of UAF reduce the rRNA synthesis rate by 70% compared to WT, and produce rRNA using both Pol I and Pol II. Miller chromatin spreads demonstrated that even though there is an overall reduction in rRNA synthesis in uaf30 mutants, the active rDNA genes in such strains are overloaded with polymerases. This phenotype was specific to defects in Uaf30, as mutations in other UAF subunits resulted in a complete absence of rDNA genes with high, or even modest Pol densities. The lack of Uaf30 prevented UAF from efficiently binding to the rDNA promoter in vivo, leading to an inability to activate a large number of rDNA genes. The relatively few genes that did become activated were highly transcribed, apparently to compensate for the reduced rRNA synthesis capacity. The results show that Uaf30p is a key targeting factor for the UAF complex that facilitates activation of a large proportion of rDNA genes in the tandem array.

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