Transcription elongation factor which binds histone H3 and enhances transcription elongation by RNA polymerase II (RNAPII). Required for the transcriptional induction of heat shock response genes and for maximal recruitment of two other elongation factors, Spt5 and Paf1, to the induced Hsp70. Plays a critical role in normal fly development throughout the lifecycle. Self associates. Interacts with RNA polymerase II. Interacts with the FACT complex, which is composed of dre4/Spt16 and Ssrp/Ssrp1. Interacts with the exosome, a complex with 3'-5' exoribonuclease activity which is composed of at least Csl4, Dis3, Mtr3, Rrp4, Rrp6, Rrp40, Rrp42, Rrp46 and Ski6. Interacts with the DRB sensitivity-inducing factor complex (the DSIF complex), which is composed of Spt4 and Spt5. Recruited to sites of active transcription where it colocalizes with the elongating form of RNA polymerase II. Belongs to the SPT6 family. Truncated N-terminus.