ABSTRACT
Histone acetyltransferases have been shown to participate in many essential cellular processes, particularly those associated with activation of transcription. SAGA (Spt-Ada-Gcn5 acetyltransferase) and SLIK (SAGA-like) are two highly homologous multisubunit histone acetyltransferase complexes that were originally identified in the yeast Saccharomyces cerevisiae. Here, we identify the protein Sgf73/Sca7 as a component of SAGA and SLIK, and a homologue of the human SCA7-encoded protein ataxin-7, which, in its polyglutamine expanded pathological form, is responsible for the neurodegenerative disease spinocerebellar ataxia 7 (SCA7). Our findings indicate that yeast Sca7 is necessary for the integrity and function of both SAGA and SLIK, and that the human ataxin-7 is able to compliment the loss of Sca7 in yeast. A polyglutamine-expanded version of ataxin-7 assembles a SAGA complex that is depleted of critical proteins that regulate the ability of SAGA to acetylate nucleosomes. These observations have significant implications for the function of the human Sca7 protein in disease pathogenesis.
Subject(s)
Acetyltransferases/genetics , Multiprotein Complexes/metabolism , Nerve Tissue Proteins/genetics , Trinucleotide Repeat Expansion/genetics , Yeasts/genetics , Amino Acid Sequence , Ataxin-7 , Blotting, Western , Histone Acetyltransferases , Molecular Sequence Data , Multiprotein Complexes/genetics , Nerve Tissue Proteins/metabolism , Peptides/genetics , Sequence Alignment , Yeasts/enzymology , beta-GalactosidaseSubject(s)
Acetyltransferases/isolation & purification , Acetyltransferases/metabolism , Acetyltransferases/genetics , Electrophoresis, Polyacrylamide Gel/methods , Histone Acetyltransferases , Humans , Indicators and Reagents , Nucleosomes/ultrastructure , Protein Denaturation , Protein Renaturation , Protein Subunits/isolation & purification , Saccharomyces cerevisiae/enzymology , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae Proteins/genetics , Saccharomyces cerevisiae Proteins/isolation & purification , Saccharomyces cerevisiae Proteins/metabolismABSTRACT
The SAGA complex is a conserved histone acetyltransferase-coactivator that regulates gene expression in Saccharomyces cerevisiae. SAGA contains a number of subunits known to function in transcription including Spt and Ada proteins, the Gcn5 acetyltransferase, a subset of TATA-binding-protein-associated factors (TAF(II)s), and Tra1. Here we report the identification of SLIK (SAGA-like), a complex related in composition to SAGA. Notably SLIK uniquely contains the protein Rtg2, linking the function of SLIK to the retrograde response pathway. Yeast harboring mutations in both SAGA and SLIK complexes displays synthetic phenotypes more severe than those of yeast with mutation of either complex alone. We present data indicating that distinct forms of the SAGA complex may regulate specific subsets of genes and that SAGA and SLIK have multiple partly overlapping activities, which play a critical role in transcription by RNA polymerase II.
