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 (By similarity). Required for the translocation of insulin-induced glucose transporter SLC2A4/GLUT4 to the cell membrane (PubMed:27354378). COPII is composed of at least five proteins: the Sec23/24 complex, the Sec13/31 complex and Sar1 (By similarity). Interacts with SEC23IP (PubMed:10400679). Interacts with HTR4 (PubMed:15466885). Interacts with SEC16A (PubMed:17428803). Interacts with SLC6A4 (PubMed:17452640). Interacts (as part of the Sec23/24 complex) with SEC22B; recruits SEC22B into COPII-coated vesicles and allows the transport of this cargo from the endoplasmic reticulum to the Golgi. Interacts (via Gelsolin-like repeat) with MIA2 and MIA3; specifically involved in the transport of large cargos like the collagen COL7A1 (By similarity). Interacts with DDHD1 (PubMed:17428803). Interacts with TMEM39A (By similarity). Interacts with SACM1L; this interaction is reduced in the absence of TMEM39A (By similarity). Interacts with kinase FAM20C; transport of FAM20C from the endoplasmic reticulum to the Golgi is likely to be mediated by COPII vesicles (By similarity). Enriched at endoplasmic reticulum exit sites (ERES), also known as transitional endoplasmic reticulum (tER). High levels in brain and fibroblasts. The Gelsolin-like repeat mediates interaction with proteins containing PPP motifs that include MIA2, MIA3 but also SEC31A. These interactions are probably competitive. Belongs to the SEC23/SEC24 family. SEC23 subfamily.