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Molecular and Cellular Biology, November 2000, p. 8343-8351, Vol. 20, No. 22
Department of Biochemistry, Division of
Nucleic Acids Enzymology, Robert Wood Johnson Medical School,
Piscataway, New Jersey 08854
Received 18 July 2000/Returned for modification 9 August
2000/Accepted 15 August 2000
SSU72 is an essential gene encoding a phylogenetically
conserved protein of unknown function that interacts with the general transcription factor TFIIB. A recessive ssu72-1 allele was
identified as a synthetic enhancer of a TFIIB (sua7-1)
defect, resulting in a heat-sensitive (Ts
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Functional Interaction between Ssu72 and the Rpb2
Subunit of RNA Polymerase II in Saccharomyces
cerevisiae
) phenotype and
a dramatic downstream shift in transcription start site selection. Here
we describe a new allele, ssu72-2, that confers a
Ts
phenotype in a SUA7 wild-type background.
In an effort to further define Ssu72, we isolated suppressors of the
ssu72-2 mutation. One suppressor is allelic to
RPB2, the gene encoding the second-largest subunit of RNA
polymerase II (RNAP II). Sequence analysis of the rpb2-100
suppressor defined a cysteine replacement of the phylogenetically invariant arginine residue at position 512 (R512C), located within homology block D of Rpb2. The ssu72-2 and
rpb2-100 mutations adversely affected noninduced gene
expression, with no apparent effects on activated transcription in
vivo. Although isolated as a suppressor of the ssu72-2
Ts
defect, rpb2-100 enhanced the
transcriptional defects associated with ssu72-2. The Ssu72
protein interacts directly with purified RNAP II in a
coimmunoprecipitation assay, suggesting that the genetic interactions
between ssu72-2 and rpb2-100 are a consequence of physical interactions. These results define Ssu72 as a highly conserved factor that physically and functionally interacts with the
RNAP II core machinery during transcription initiation.
*
Corresponding author. Mailing address: Department of
Biochemistry, Robert Wood Johnson Medical School, 675 Hoes Lane,
Piscataway, NJ 08854. Phone: (732) 235-5888. Fax: (732) 235-5889. E-mail: hampsemi{at}umdnj.edu.
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