Figure 1.

The biogenesis of the M13 procoat and H1-procoat proteins in E. coli. The major coat protein of bacteriophage M13 is synthesized as a 73-aa precursor (procoat) that contains a typical cleaved leader sequence (green). Wild-type procoat (A) appears to insert into the inner membrane spontaneously. The insertion of H1-procoat (B), a procoat derivative that contains an extremely hydrophobic leader sequence (red), depends on both the cotranslational SRP targeting pathway and the SecY translocation complex. The modification of the leader presumably prevents direct insertion by either changing the physical properties of the molecule or increasing the probability of aggregation in the cytoplasm.