<p>This family consists of several eukaryotic nuclear transcription elongation proteins characterised by an extremely acidic N-terminal region. In yeast, increased or decreased dosage of Spt6 protein can change gene expression [<cite idref="PUB00027930"/>]. In addition, all members contain a YqgFc domain. This domain is found primarily in low-GC Gram-positive bacteria Holliday junction resolvases. However, in Spt6 orthologues, the catalytic residues are substituted, indicating that they lack resolvase activity. Some members contain a copy of the S1 domain (<db_xref db="INTERPRO" dbkey="IPR003029"/>) that occurs in a wide range of RNA associated proteins. It is structurally similar to cold shock protein, which binds nucleic acids. The S1 domain has an OB-fold structure. Adjacent to this domain one to two copies of the SH2 domain are present (<db_xref db="INTERPRO" dbkey="IPR000980"/>) which are regulatory modules of signal cascades.</p> <p>Three transcription-elongation factors--Spt4, Spt5, and Spt6--are conserved among eukaryotes and are essential for transcription via modulation of chromatin structure. Spt4 and Spt5 are tightly associated in a complex, while the physical association of 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 [<cite idref="PUB00012261"/>].</p>