Biosynthesis of intestinal microvillar proteins. Translational evidence in vitro that aminopeptidase N is synthesized as a Mr-115000 polypeptide

Abstract

A crude RNA fraction, prepared from pig small intestine, was more efficient than a fraction enriched in polyadenylated RNA in directing translation of polypeptides with MW > 100,000 in a rabbit reticulocyte lysate system. Aminopeptidase N synthesized in vitro was immunopurified from the translation mixture and analyzed by sodium dodecyl sulfate/polyacrylamide-gel electrophoresis. It had an apparent MW of 115,000 regardless of whether the translation was performed in the absence or presence of proteinase inhibitors. This result contradicts the possibility of aminopeptidase N being synthesized as a large single-chain precursor polypeptide.