An amino acid sequence which directs membrane insertion causes loss of membrane potential.

A 55-amino acid segment, normally present between residues 241 and 295 of the 348-residue gene I protein of the filamentous bacteriophage f1, acts as an internal signal sequence for gene I protein or, when present in fusion proteins, for EcoRI endonuclease or alkaline phosphatase. The resulting proteins are inserted so that they span the membrane with sequences on the amino side of the 55-residue segment in the cytoplasm and those near the carboxy side outside the cytoplasmic membrane. The presence of these proteins in the membrane results in the rapid inhibition of cell growth, probably from a loss of the membrane potential. We describe some of the elements in this 55-residue segment that appear to be crucial for its interaction with the membrane.