Proline rich acidic protein 1 (PRAP1) is also named as PRO1195 or UPA. It may play an important role in maintaining normal growth homeostasis in epithelial cells. Mitotic arrest deficient 1 (MAD1) is a key component in mitotic checkpoint signaling. Recent study identified PRAP1 as a novel MAD1 binding partner using yeast-two hybrid screening. PRAP1 has four isoforms with MW 16-20 kDa and 10 kDa.