Tra1 has specific regulatory roles, rather than global functions, within the SAGA co-activator complex

The SAGA complex is a conserved, multifunctional coactivator that has broad roles in eukaryotic transcription. Previous studies suggested that Tra1, the largest SAGA component, is required either for SAGA assembly or for SAGA recruitment by DNA-bound transcriptional activators. In contrast to Saccharomyces cerevisiae and mouse, a tra1 Delta mutant is viable in Schizosaccharomyces pombe, allowing us to test these issues in vivo. We find that, in a tra1D mutant, SAGA assembles and is recruited to some, but not all, promoters. Consistent with these findings, Tra1 regulates the expression of only a subset of SAGA-dependent genes. We previously reported that the SAGA sub-units Gcn5 and Spt8 have opposing regulatory roles during S. pombe sexual differentiation. We show here that, like Gcn5, Tra1 represses this pathway, although by a distinct mechanism. Thus, our study reveals that Tra1 has specific regulatory roles, rather than global functions, within SAGA. The EMBO Journal ( 2011) 30, 2843-2852. doi:10.1038/emboj.2011.181; Published online 3 June 2011