Identification of the gal4 suppressor Sug1 as a subunit of the yeast 26S proteasome.
The SUG1 gene of Saccharomyces cerevisiae encodes a putative ATPase. Mutations in SUG1 were isolated as suppressors of a mutation in the transcriptional activation domain of GAL4. Sug1 was recently proposed to be a subunit of the RNA polymerase II holoenzyme and to mediate the association of transcriptional activators with holoenzyme. We show here that Sug1 is not a subunit of the holoenzyme, at least in its purified form, but of the 26S proteasome, a large complex of relative molecular-mass 2,000K that catalyses the ATP-dependent degradation of ubiquitin-protein conjugates. Sug1 co-purifies with the proteasome in both conventional and nickel-chelate affinity chromatography. Our observations account for the reduced ubiquitin-dependent proteolysis in sug1 mutants and suggest that the effects of sug1 mutations on transcription are indirect results of defective proteolysis.
Rubin
D M
DM
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Coux
O
O
Wefes
I
I
Hengartner
C
C
Young
R A
RA
Goldberg
A L
AL
Finley
D
D
D000251:Adenosine Triphosphatases; D000595:Amino Acid Sequence; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000032:analysis* / Q000235:genetics; D008969:Molecular Sequence Data; D010447:Peptide Hydrolases / Q000737:chemistry* / Q000235:genetics; D046988:Proteasome Endopeptidase Complex; D012097:Repressor Proteins / Q000032:analysis* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D000251:Adenosine Triphosphatases; C069670:RPT6 protein, S cerevisiae