Conversion of beta-galactosidase to a membrane-bound state by gene fusion.

Abstract

A series of [Escherichia coli] strains was isolated in which the lacZ gene was fused to 1 of the maltose operons, such that the synthesis of .beta.-galactosidase (.beta.-D-galactoside galactohydrolase; EC 3.2.1.23) is inducible by maltose. The most frequent event that generates such fusions results in strains in which an intact lacZ gene has become a part of the malE, F operon. By using a special selection procedure, much rarer fusion events resulting in an altered .beta.-galactosidase molecule are detected. In these strains, there is probably a hybrid protein molecule produced, comprised of an NH2-terminal amino acid sequence from a maltose transport protein (malF) and a COOH-terminal amino acid sequence from .beta.-galactosidase. The hybrid protein, which still retains some .beta.-galactosidase activity, is found in the cytoplasmic membrane. These results provide information on the component of the malF gene essential for incorporation of its product into the membrane.