This family consists of several eukaryotic transcription elongation Spt4 proteins as well as archaebacterial RpoE2. Three transcription-elongation factors Spt4, Spt5, and Spt6 are conserved among eukaryotes and are essential for transcription via the modulation of chromatin structure. Spt4 and Spt5 are tightly associated in a complex, while the physical association of the Spt4-Spt5 complex with Spt6 is considerably weaker. It has been demonstrated that Spt4, Spt5, and Spt6 play roles in transcription elongation in both yeast and humans including a role in activation by Tat. It is known that Spt4, Spt5, and Spt6 are general transcription-elongation factors, controlling transcription both positively and negatively in important regulatory and developmental roles. RpoE2 is one of 13 subunits in the archaeal RNA polymerase. These proteins contain a C4-type zinc finger, and the structure has been solved in. The structure reveals that Spt4-Spt5 binding is governed by an acid-dipole interaction between Spt5 and Spt4, and the complex binds to and travels along the elongating RNA polymerase. The Spt4-Spt5 complex is likely to be an ancient, core component of the transcription elongation machinery.