Previously we reported [Deane, S. M., Maharaj, R., Robb, F. T. & Woods, D. R. (1987) Journal of General Microbiology 133, 2295-2302] that the production of a Vibrio alginolyticus SDS-resistant alkaline serine protease (Pro A) cloned in Escherichia coli was characterized by a 12 h delay between the synthesis of an inactive precursor and secretion of active Pro A. Replacement of the V. alginolyticus promoter region by the alpha-amylase promoter region from Bacillus amyloliquefaciens resulted in the simultaneous synthesis and secretion of Pro A in E. coli. The V. alginolyticus pro A gene cloned on a shuttle vector did not produce active Pro A in Bacillus subtilis. Although Pro A has a typical Gram-positive signal sequence, it was not functional in B. subtilis. Replacement of the Pro A signal sequence with the alpha-amylase signal sequence resulted in the production of active Pro A in B. subtilis.