Involved in protein export. Part of the protein translocation apparatus. Forms complexes with SecD. A double secD and secF deletion grows very poorly on solid medium at 45 degrees Celsius, confers a severe cold-sensitive growth phenotype (30 degrees Celsius), as well as having defects in Sec-dependent protein translocation. Has no effects on Sec-independent Tat substrate protein export. Belongs to the SecD/SecF family. SecF subfamily.