Required for the insertion and/or proper folding and/or complex formation of integral membrane proteins into the membrane. Involved in integration of membrane proteins that insert both dependently and independently of the Sec translocase complex, as well as at least some lipoproteins. Aids folding of multispanning membrane proteins (By similarity). Probably also aids protein insertion, folding and/or assembly of membrane complexes destined for the thylakoid. Interacts with the Sec translocase complex via SecD. Specifically interacts with transmembrane segments of nascent integral membrane proteins during membrane integration (By similarity). Belongs to the OXA1/ALB3/YidC family. Type 1 subfamily.