Transcriptional repressor that may play a role in the specification and differentiation of lung epithelium. May also play a role in developing neural, gastrointestinal and cardiovascular tissues. Can act with CTBP1 to synergistically repress transcription but CTPBP1 is not essential. Plays a role in synapse formation by regulating SRPX2 levels (By similarity). Forms homodimers and heterodimers with FOXP1 and FOXP4. Dimerization is required for DNA-binding. Interacts with CTBP1 (By similarity). Interacts with FOXP1 (By similarity). Interacts with TBR1 (By similarity). Interacts with ZMYM2 (By similarity). The leucine-zipper is required for dimerization and transcriptional repression.