Variable specific activity of Escherichia coli beta-galactosidase in bacterial cells

Escherichia coil lacZ is a frequently employed reporter gene for the monito ring of gene expression and recombinant protein production due the simple d etermination of beta -galactosidase activity in both qualitative and quanti tative assays. In the absence of either total or recombinant protein synthe sis, we observed a lack of correlation between protein amount and enzymatic activity in both engineered and native beta -galactosidases in Escherichia coli cells. A delayed fading of beta -galactosidase activity compared with the rapid degradation of intact protein suggests a progressive increase in enzyme-specific activity during the life of the protein. This intriguing e vent does not involve solubilization from major protein aggregates and it o ccurs both in vivo and in cell extracts, but not in solutions of purified p rotein. Possible explanations for this activation are examined in the conte xt of the assisted protein folding network and proteolytic degradation of m isfolded proteins. (C) 2001 John Wiley & Sons, Inc.