Component of the transcription complexes of the pulmonary surfactant-associated protein-B (SFTPB) and -C (SFTPC). Enhances homeobox protein Nkx-2.1-activated SFTPB and SFTPC promoter activities. Interacts with NKX2-1. Ubiquitously expressed. In lung, expression is restricted to the alveolar epithelial cells. Belongs to the TAP26 family.