M13 procoat and a pre-immunoglobulin share processing specificity but use different membrane receptor mechanisms.

Bacteriophage M13 procoat is accurately processed to transmembrane coat protein by salt-washed or N-ethylmaleimide-treated rough microsomes from dog pancreas. These treatments inhibit the processing of eukaryotic secreted protein precursors. M13 procoat can assemble into dog pancreas microsomes post-translationally. Thus, the microsomal proteins needed for assembly may be determined by the nature of the precursor protein itself. These results, and our finding that the mouse IgG kappa chain fragment precursor is processed by Escherichia coli leader peptidase, also suggest that the cleavage specificity of leader (signal) peptidases and the properties of preproteins that render them suitable for cleavage have been conserved during evolution.