SAGA is a transcriptional coactivator complex that is conserved across 
eukaryotes and performs multiple functions during transcriptional activation and 
elongation. One role is deubiquitination of histone H2B, and this activity 
resides in a distinct subcomplex called the deubiquitinating module (DUBm), 
which contains the ubiquitin-specific protease Ubp8, bound to Sgf11, Sus1, and 
Sgf73. The deubiquitinating activity depends on the presence of all four DUBm 
proteins. We report here the 1.90 angstrom resolution crystal structure of the 
DUBm bound to ubiquitin aldehyde, as well as the 2.45 angstrom resolution 
structure of the uncomplexed DUBm. The structure reveals an arrangement of 
protein domains that gives rise to a highly interconnected complex, which is 
stabilized by eight structural zinc atoms that are critical for enzymatic 
activity. The structure suggests a model for how interactions with the other 
DUBm proteins activate Ubp8 and allows us to speculate about how the DUBm binds 
to monoubiquitinated histone H2B in nucleosomes.