The Something About Silencing protein, Sas3, is the catalytic subunit of NuA3, a yTAF(II)30-containing HAT complex that interacts with the Spt16 subunit of the yeast CP (Cdc68/Pob3)-FACT complex

We have purified and characterized a Gen5-independent nucleosomal histone H 3 HAT complex, NuA3 (Nucleosomal Acetyltransferase of histone H3). Peptide sequencing of proteins from the purified NuA3 complex identified Sas3 as th e catalytic HAT subunit of the complex. Sas3 is the yeast homolog of the hu man MOZ oncogene. Sas3 is required for both the HAT activity and the integr ity of the NuA3 complex. In addition, NuA3 contains the TBP- associated fac tor, yTAF(II)30, which is also a component of the TFIID, TFIIF, and SWI/SNF complexes. Sas3 mediates interaction of the NuA3 complex with Spt16 both i n vivo and in vitro. Spt16 functions as a component of the yeast CP (Cdc68/ Pob3) and mammalian FACT (facilitates chromatin transcription) complexes, w hich are involved in transcription elongation and DNA replication. This int eraction suggests that the NuA3 complex might function in concert with FACT -CP to stimulate transcription or replication elongation through nucleosome s by providing a coupled acetyltransferase activity.