Subunit of the protein translocation channel SecYEG. The function of the beta subunit is unknown, but it may be involved in stabilization of the trimeric complex. Component of the Sec protein translocase complex. Heterotrimer consisting of alpha (SecY), beta (SecG) and gamma (SecE) subunits. The heterotrimers can form oligomers, although 1 heterotrimer is thought to be able to translocate proteins. Interacts with the ribosome. May interact with SecDF, and other proteins may be involved. Belongs to the SEC61-beta family.