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. SEC23 interacts with BET3 in order to target TRAPPI complex to COPII involved in internalization of plasma membrane proteins like the maltose transporter. The COPII coat is composed of at least 7 proteins: the SEC23/24 complex, the SEC13/31 complex, SFB2, SFB3 and the protein SAR1. Forms two other heterodimeric complexes with SFB3 and PDR17. Interacts with BET1, BET3, BOS1, EMP24, GRH1, SEC16, SEC22 and SYS1. Ubiquitinated. Ubiquitination is required for the formation of the SEC23/24 complex. Deubiquitinated by the UBP3/BRE5 complex. Belongs to the SEC23/SEC24 family. SEC23 subfamily.