Probable transcriptional activator. Component of the PCAF complex, at least composed of TADA2L/ADA2, SUPT3H, TADA3L/ADA3, TAF5L/PAF65-beta, TAF6L/PAF65-alpha, TAF10/TAFII30, TAF12/TAFII20, TAF9/TAFII31 and TRRAP. Associates with TAFII31 and GCN5L2. Component of the TFTC-HAT complex, at least composed of TAF5L, TAF6L, TADA3L, SUPT3H/SPT3, TAF2/TAFII150, TAF4/TAFII135, TAF5/TAFII100, GCN5L2/GCN5, TAF10 and TRRAP. Component of the STAGA transcription coactivator-HAT complex, at least composed of SUPT3H, GCN5L2, TAF5L, TAF6L, SUPT7L, TADA3L, TAD1L, TAF10, TAF12, TRRAP and TAF9. The STAGA core complex is associated with a subcomplex required for histone deubiquitination composed of ATXN7L3, ENY2 and USP22. Expressed in all tissues tested including pancreas, kidney, skeletal muscle, liver, lung, placenta, brain and heart. Belongs to the SPT3 family. Extended N-terminus. Chimeric cDNA.