May have a special functional role during embryogenesis and in adult hematopoietic cells. Binds to ubiquitin. Preferentially expressed in adult hematopoietic tissues. High levels in lymphoid and myeloid tissues. Highly expressed in peripheral blood leukocytes, thymus, spleen and lung, followed by placenta, liver and kidney. By retinoic acid. Belongs to the LAPTM4/LAPTM5 transporter family.