This is the very acidic N-terminal region of the early transcription elongation factor Spt5 [1]. The Spt5-Spt4 complex regulates early transcription elongation by RNA polymerase II and has an imputed role in pre-mRNA processing via its physical association with mRNA capping enzymes. The actual function of this N-terminal domain is not known although it is dispensable for binding to Spt4 [2].

1: Novel domains and orthologues of eukaryotic transcription elongation factors. Ponting CP; Nucleic Acids Res. 2002;30:3643-3652. PMID:12202748

2: Characterization of the Schizosaccharomyces pombe Spt5-Spt4 complex. Schwer B, Schneider S, Pei Y, Aronova A, Shuman S; RNA. 2009; [Epub ahead of print] PMID:19460865