Functional organization of the yeast SAGA complex: distinct components involved in structural integrity, nucleosome acetylation, and TATA-binding protein interaction.
SAGA, a recently described protein complex in Saccharomyces cerevisiae, is important for transcription in vivo and possesses histone acetylation function. Here we report both biochemical and genetic analyses of members of three classes of transcription regulatory factors contained within the SAGA complex. We demonstrate a correlation between the phenotypic severity of SAGA mutants and SAGA structural integrity. Specifically, null mutations in the Gcn5/Ada2/Ada3 or Spt3/Spt8 classes cause moderate phenotypes and subtle structural alterations, while mutations in a third subgroup, Spt7/Spt20, as well as Ada1, disrupt the complex and cause severe phenotypes. Interestingly, double mutants (gcn5Delta spt3Delta and gcn5Delta spt8Delta) causing loss of a member of each of the moderate classes have severe phenotypes, similar to spt7Delta, spt20Delta, or ada1Delta mutants. In addition, we have investigated biochemical functions suggested by the moderate phenotypic classes and find that first, normal nucleosomal acetylation by SAGA requires a specific domain of Gcn5, termed the bromodomain. Deletion of this domain also causes specific transcriptional defects at the HIS3 promoter in vivo. Second, SAGA interacts with TBP, the TATA-binding protein, and this interaction requires Spt8 in vitro. Overall, our data demonstrate that SAGA harbors multiple, distinct transcription-related functions, including direct TBP interaction and nucleosomal histone acetylation. Loss of either of these causes slight impairment in vivo, but loss of both is highly detrimental to growth and transcription.
Sterner
D E
DE
The Wistar Institute, Philadelphia, Pennsylvania 19104, USA.
Grant
P A
PA
Roberts
S M
SM
Duggan
L J
LJ
Belotserkovskaya
R
R
Pacella
L A
LA
Winston
F
F
Workman
J L
JL
Berger
S L
SL
D000107:Acetylation; D000123:Acetyltransferases / Q000235:genetics / Q000502:physiology; D048868:Adaptor Proteins, Signal Transducing; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051548:Histone Acetyltransferases; D046911:Macromolecular Substances; D016296:Mutagenesis; D009707:Nucleosomes; D010641:Phenotype; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D035181:TATA-Box Binding Protein; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000099224:p300-CBP-Associated Factor
D000123:Acetyltransferases; D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D051548:Histone Acetyltransferases; D046911:Macromolecular Substances; D009707:Nucleosomes; D011494:Protein Kinases; D029701:Saccharomyces cerevisiae Proteins; D035181:TATA-Box Binding Protein; D015534:Trans-Activators; D014157:Transcription Factors; C090575:ADA2 protein, S cerevisiae; C106162:HFI1 protein, S cerevisiae; C099690:SPT20 protein, S cerevisiae; C075582:SPT3 protein, S cerevisiae; C093107:SPT7 protein, S cerevisiae; C089445:SPT8 protein, S cerevisiae; C501392:GCN5 protein, S cerevisiae; D000099224:p300-CBP-Associated Factor