Mutations affecting a regulated, membrane-associated esterase in Salmonella typhimurium LT2

Area of Science:

• Microbiology
• Bacterial genetics
• Enzyme regulation

Background:

• Salmonella typhimurium apeA mutations result in the loss of a soluble enzyme, protease I.
• This enzyme normally hydrolyzes specific chromogenic substrates.

Purpose of the Study:

• To investigate the genetic basis of pseudorevertants that regain esterase activity.
• To characterize the regulatory mechanism of a novel membrane-bound esterase.

Main Methods:

• Isolation and genetic analysis of Salmonella typhimurium pseudorevertants.
• Phage P1 transduction mapping to determine locus linkage.
• Construction of apeE-lacZ operon fusion strains to assess gene expression.

Main Results:

• Pseudorevertants of apeA mutations acquired mutations at the apeR locus.
• The apeR locus controls the overproduction of a distinct membrane-bound esterase (ApeE).
• apeR mutations significantly increase apeE expression, indicating ApeR acts as a repressor.

Conclusions:

• The apeR locus encodes a repressor protein that regulates the expression of the apeE gene.
• The ApeE protein, a membrane-associated esterase, is distinct from the soluble protease I.
• Evidence suggests the ApeE protein functions as an esterase, not a protease.