Part of the Ssh1 complex, which probably is the major component of a channel-forming translocon complex that may function exclusively in the cotranslational pathway of protein endoplasmic reticulum (ER) import. Component of the heterotrimeric Ssh1 complex, which is composed of SSH1, SBH2 and SSS1. Present with 704 molecules/cell in log phase SD medium. Belongs to the SecY/SEC61-alpha family.