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Molecular and Cellular Biology, April 2000, p. 2455-2465, Vol. 20, No. 7
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Genetic Analysis of the Ydr1-Bur6 Repressor Complex Reveals an Intricate Balance among Transcriptional Regulatory Proteins in Yeast

Sungjoon Kim,1,2 Kettly Cabane,1,2 Michael Hampsey,2 and Danny Reinberg1,2,*

Howard Hughes Medical Institute,1 Division of Nucleic Acids Enzymology,2 Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854-5635

Received 1 December 1999/Returned for modification 4 January 2000/Accepted 13 January 2000

A transcriptional repressor complex encoded by two essential genes, YDR1 and BUR6, was isolated from Saccharomyces cerevisiae and shown to be the functional counterpart of the human repressor complex Dr1-DRAP1. To elucidate the mechanism of repression by this complex, altered forms of Ydr1 and Bur6 were studied in vitro and in vivo. Deletion of the C-terminal 41 amino acids of Ydr1 resulted in loss of repressor activity and a growth defect, suggesting that the C-terminal domain of Ydr1 functions as a potent transcriptional repressor. A screen for extragenic suppressors of a cold-sensitive ydr1 (ydr1cs) mutant led to the identification of recessive mutations in the SIN4 gene, which encodes a component of the SRB-MED complex. The sin4 alleles suppressed not only ydr1cs mutations but also bur6cs mutations. In contrast, deletion of the gal11 gene, whose product is also a member of the SRB-MED complex, failed to suppress ydr1cs and bur6cs mutations, indicating that suppression is not due to general defects in the SRB-MED complex. Moreover, one of the sin4 alleles, but not the sin4 deletion, was found to specifically suppress the inviability of a ydr1 deletion, demonstrating that the essential function of Ydr1 becomes dispensable in a sin4 mutant background. Biochemical analysis of the SRB-MED complex from the sin4 suppressor strain revealed a structurally distinct form of the SRB-MED complex that lacks a subset of mediator subunits. These results define a delicate balance between positive and negative regulators of transcription operating through the Ydr1-Bur6 repressor complex.

* Corresponding author. Mailing address: Howard Hughes Medical Institute, Department of Biochemistry, Robert Wood Johnson Medical School, 663 Hoes Ln., Piscataway, NJ 08854-5635. Phone: (732) 235-4195. Fax: (732) 235-5294. E-mail: reinbedf{at}umdnj.edu.

Molecular and Cellular Biology, April 2000, p. 2455-2465, Vol. 20, No. 7
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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