Component of the coat protein complex II (COPII) which promotes the formation of transport vesicles from the endoplasmic reticulum (ER). The coat has two main functions, the physical deformation of the endoplasmic reticulum membrane into vesicles and the selection of cargo molecules for their transport to the Golgi complex (PubMed:10214955, PubMed:17499046, PubMed:18843296, PubMed:20427317). Plays a central role in cargo selection within the COPII complex and together with SEC24D may have a different specificity compared to SEC24A and SEC24B (PubMed:17499046, PubMed:20427317, PubMed:18843296). May more specifically package GPI-anchored proteins through the cargo receptor TMED10 (PubMed:20427317). May also be specific for IxM motif-containing cargos like the SNAREs GOSR2 and STX5 (PubMed:18843296). COPII is composed of at least five proteins: the Sec23/24 complex, the Sec13/31 complex and Sar1 (PubMed:10214955, PubMed:10075675, PubMed:17499046). Interacts with TMED2 and TMED10 (PubMed:20427317). Interacts with GOSR2 (via IxM motif) and STX5 (via IxM motif); recruits GOSR2 and STX5 into COPII-coated vesicles (PubMed:18843296). Interacts with DDHD1 (PubMed:17428803). Interacts with STING1; promoting STING1 translocation to the COPII vesicles (PubMed:30842662). Ubiquitous. Belongs to the SEC23/SEC24 family. SEC24 subfamily.