Transcription and mRNA export are linked processes. However, the molecular 
mechanisms of this coordination are not clear. Sus1 (hENY2) participates in this 
coordination as part of two protein complexes: SAGA, a transcriptional 
co-activator; TREX-2, which functions in mRNA biogenesis and export. Here, we 
investigate the coordinated action of SAGA and TREX-2 required for gene 
expression. We demonstrate that TREX-2 subunit Sem1 also participates in 
transcription activation. Like Sus1, Sem1 is required for the induction of ARG1 
and GAL1, these being SAGA-regulated genes. Chromatin immunoprecipitations show 
that proper recruitment of certain SAGA subunits to the GAL1 promoter depends on 
Sem1. Notably, both in vivo and in vitro analyses reveal that Sem1 influences 
SAGA-dependent histone H2B deubiquitylation. Most of these phenotypes are also 
found to depend on another TREX-2 subunit, Thp1. These results unveil a new role 
for Sem1 in the activation of the SAGA-dependent gene GAL1 and influencing H2B 
deubiquitylation. Our work provides insights into a novel functional 
relationship between Sem1 and the SAGA complex.