Component of the PAT complex, an endoplasmic reticulum (ER)-resident membrane multiprotein complex that facilitates multi-pass membrane proteins insertion into membranes. The PAT complex acts as an intramembrane chaperone by directly interacting with nascent transmembrane domains (TMDs), releasing its substrates upon correct folding, and is needed for optimal biogenesis of multi-pass membrane proteins. WDR83OS/Asterix is the substrate-interacting subunit of the PAT complex, whereas CCDC47 is required to maintain the stability of WDR83OS/Asterix. WDR83OS/Asterix associates with the first transmembrane domain (TMD1) of the nascent chain, independently of the N-glycosylation of the chain and irrespective of the amino acid sequence and transmembrane topology of TMD1. The PAT complex favors the binding to TMDs with exposed hydrophilic amino acids within the lipid bilayer and provides a membrane-embedded partially hydrophilic environment in which TMD1 binds. Component of the PAT complex. Expressed in the early neural plate of embryos. Expressed in the hypoblast and Koller's sickle at pre-primitive streak stages. At stage 4, expression is detected in the node, the lips of the streak and the epiblast in the middle of the area pellucida. By the start of neurulation, expression becomes progressively concentrated in the neural plate, neural tube and sensory placodes including lens, otic and olfactory placodes. Expressed in the notochord and the sensory placodes at stage 16. Expressed in somites and persists in the myotome at later stages. Up-regulated by FGF. Belongs to the Asterix family.