The use ofBacillus amyloliquefaciensfor enzyme production and its exceptional highprotein export capacity initiated this study where the presence and function of multiple type I signal peptidase isoforms was investigated. In addition to type I signal peptidases SipS(ba) [Meijer,., de Jong,A., Bea, G., Wisman, A., Tjalsma, H., Venema, G., Bron, S. & van Dijl, . (1995)Mol. , 621±631] and SipT(ba) [Hoang, V. & Hofemeister, J. (1995) Biochim. Biophys.