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Molecular and Cellular Biology, July 2004, p. 6419-6429, Vol. 24, No. 14
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.14.6419-6429.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

TATA-Binding Protein Mutants That Are Lethal in the Absence of the Nhp6 High-Mobility-Group Protein

Peter Eriksson,{dagger} Debabrata Biswas, Yaxin Yu, James M. Stewart, and David J. Stillman*

Department of Pathology, University of Utah Health Sciences Center, Salt Lake City, Utah 84132

Received 26 November 2003/ Returned for modification 9 January 2004/ Accepted 20 April 2004

The Saccharomyces cerevisiae Nhp6 protein is related to the high-mobility-group B family of architectural DNA-binding proteins that bind DNA nonspecifically but bend DNA sharply. Nhp6 is involved in transcriptional activation by both RNA polymerase II (Pol II) and Pol III. Our previous genetic studies have implicated Nhp6 in facilitating TATA-binding protein (TBP) binding to some Pol II promoters in vivo, and we have used a novel genetic screen to isolate 32 new mutations in TBP that are viable in wild-type cells but lethal in the absence of Nhp6. The TBP mutations that are lethal in the absence of Nhp6 cluster in three regions: on the upper surface of TBP that may have a regulatory role, near residues that contact Spt3, or near residues known to contact either TFIIA or Brf1 (in TFIIIB). The latter set of mutations suggests that Nhp6 becomes essential when a TBP mutant compromises its ability to interact with either TFIIA or Brf1. Importantly, the synthetic lethality for some of the TBP mutations is suppressed by a multicopy plasmid with SNR6 or by an spt3 mutation. It has been previously shown that nhp6ab mutants are defective in expressing SNR6, a Pol III-transcribed gene encoding the U6 splicing RNA. Chromatin immunoprecipitation experiments show that TBP binding to SNR6 is reduced in an nhp6ab mutant. Nhp6 interacts with Spt16/Pob3, the yeast equivalent of the FACT elongation complex, consistent with nhp6ab cells being extremely sensitive to 6-azauracil (6-AU). However, this 6-AU sensitivity can be suppressed by multicopy SNR6 or BRF1. Additionally, strains with SNR6 promoter mutations are sensitive to 6-AU, suggesting that decreased SNR6 RNA levels contribute to 6-AU sensitivity. These results challenge the widely held belief that 6-AU sensitivity results from a defect in transcriptional elongation.


* Corresponding author. Mailing address: Department of Pathology, University of Utah, 30 North 1900 East, Salt Lake City, UT 84132-2501. Phone: (801) 581-5429. Fax: (801) 581-4517. E-mail: david.stillman{at}path.utah.edu.

{dagger} Present address: National Institutes of Health, Bethesda, MD 20892.


Molecular and Cellular Biology, July 2004, p. 6419-6429, Vol. 24, No. 14
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.14.6419-6429.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.




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