MUTATIONS AFFECTING A REGULATED, MEMBRANE-ASSOCIATED ESTERASE IN SALMONELLA-TYPHIMURIUM LT2

Mutations at the apeA locus in Salmonella typhimurium lead to loss of a soluble enzyme (''protease I'') that hydrolyzes the chromogenic endo protease substrate N-acetyl phenylalanine beta-naphthyl ester. We have isolated pseudorevertants of S. typhimurium apeA mutations that have regained the ability to hydrolyze this compound. These pseudorevertant s contain mutations (apeR) that lead to overproduction of a membrane-b ound esterase different from protease I. The apeR locus is phage P1 co transducible with ilvC (83 map units) and is unlinked to apeA. Mutatio ns at still another locus, apeE, lead to loss of the membrane-associat ed esterase. The apeE locus is P1 cotransducible with purE (12 map uni ts). In an apeE-lacZ operon fusion strain, an apeR mutation increases the level of beta-galactosidase apgroximately 60-fold. We propose that apeR encodes a repressor of apeE. The evidence available suggests tha t the ApeE protein is not a protease.