Spt3 and Spt8 are involved in the formation of a silencing boundary by interacting with TATA-binding protein

In Saccharomyces cerevisiae, a heterochromatin-like chromatin structure called the silencing region is present at the telomere as a complex of Sir2, Sir3, and Sir4. Sir2 is a histone deacetylase, and Sir3 and Sir4 promote spreading of the silencing region at the telomere. Histone acetyltransferases restrict the silencing region. Here, we show that Spt3 and Spt8 block the spread of silencing regions. Spt3 and Spt8 are members of the Spt-Ada-Gcn5-acetyltransferase (SAGA) complex, which has histone acetyltransferase activity. Although both Spt3 and Spt8 interact with telomere-binding proteins (TBPs), Spt3 had a greater effect on genome-wide transcription. Mutant analysis showed that TBPs play an important role in boundary formation, in particular the interaction between Spt3 and TBPs.