The molecular organization of the yeast transcriptional coactivator Spt-Ada-Gcn5 
acetyltransferase (SAGA) was analyzed by single-particle electron microscopy. 
Complete or partial deletion of the Sgf73 subunit disconnects the 
deubiquitination (DUB) module from SAGA and favors in our conditions the 
cleavage of the C-terminal ends of the Spt7 subunit and the loss of the Spt8 
subunit. The structural comparison of the wild-type SAGA with two deletion 
mutants positioned the DUB module and enabled the fitting of the available 
atomic models. The localization of the DUB module close to Gcn5 defines a 
chromatin-binding interface within SAGA, which could be demonstrated by the 
binding of nucleosome core particles. The TATA-box binding protein 
(TBP)-interacting subunit Spt8 was found to be located close to the DUB but in a 
different domain than Spt3, also known to contact TBP. A flexible protein arm 
brings both subunits close enough to interact simultaneously with TBP.