Mapping of the transcriptional repression domain of the lymphoid-specific transcription factor oct-2A.

The lymphoid-specific transcription factor Oct-2a is implicated in B cell-specific transcriptional activity via the octamer motif. Structure/function analysis of various Oct-2a effector regions in the context of the GAL4 DNA-binding domain revealed that Oct-2a contains two functionally different activation domains at the N and the C termini. The transcriptional activity of both domains is strongly potentiated by interactions with distinct B cell-specific coactivators. Recently, we have identified a repression domain located within the N terminus of Oct-2a (amino acids 2-99). When this domain was transferred to a potent activator, transcription was strongly inhibited. In this study we present a deletion analysis of the N-terminal region of Oct-2a to determine the minimal repression domain. We identified a stretch of 23 amino acids, rich in serine and threonine residues, which was responsible for most of the repression activity. We show that repression is strongly dependent on the type of enhancer present in the reporter plasmid as well as on the cell line tested. The possibility that Oct-2a can act as an activator and/or a repressor may have important consequences for the function of Oct-2a in B cell differentiation and other developmental processes.