ASSEMBLY OF EUKARYOTIC CLASS-III (N-OUT, C-IN) MEMBRANE-PROTEINS INTOTHE ESCHERICHIA-COLI CYTOPLASMIC MEMBRANE

Class III membrane proteins lack cleavable signal peptides but adopt a n N-out, C-in topology with respect to their native membranes. We have analysed the fate of two eukaryotic class III plasma membrane protein s, human erythrocyte glycophorin C and influenza A virus M2 protein, i n Escherichia coli. The N-terminal domains of both proteins were effic iently localised to the extracytoplasmic side of the bacterial cytopla smic membrane. When beta-lactamase was fused to the C-terminus of glyc ophorin C it was localised to the cytoplasm, and protease treatment of spheroplasts caused a reduction in size of the fusion protein consist ent with glycophorin C adopting its native topology in E. coli.