Substrate adapter for ufmylation, the covalent attachment of the ubiquitin-like modifier UFM1 to substrate proteins, which plays a key role in reticulophagy (also called ER-phagy) (By similarity). In response to endoplasmic reticulum stress, promotes recruitment of the E3 ufm1-protein ligase ufl1 to the endoplasmic reticulum membrane, leading to ufmylation of target proteins and subsequent reticulophagy of endoplasmic reticulum sheets (By similarity). Plays a role in cartilage development through sox9, inhibiting the ubiquitin-mediated proteasomal degradation of this transcriptional regulator (PubMed:28263186). Localizes to the endoplasmic reticulum membrane in response to endoplasmic reticulum stress. Morpholino knockdown alters craniofacial cartilage development. Belongs to the DDRGK1 family.