Escherichia coli mutants accumulating the precursor of a secreted protein in the cytoplasm.

The maltose binding protein of Escherichia coli is secreted into the external periplasmic compartment of the cell. This article describes a selection procedure for the isolation of mutants which fail to export this protein. These mutants probably result from alterations in the amino terminal 'signal sequence', causing the maltose binding protein produced to accumulate in the cytoplasm in its precursor form.