The C-terminal domain of the transcription elongation factor protein Spt5 is necessary for binding to Spt4 to form the functional complex that regulates early transcription elongation by RNA polymerase II. The complex may be involved in pre-mRNA processing through its association with mRNA capping enzymes. This CTD domain carries a regular nonapeptide repeat that can be present in up to 18 copies, as in S. pombe. The repeat has a characteristic TPA motif.