Efficient cleavage and segregation of nascent presecretory proteins in a reticulocyte lysate supplemented with microsomal membranes.

The mRNA-dependent rabbit reticulocyte lysate of Pelham and Jackson (Pelham, H. R. B., and Jackson, R. J. (1976) Eur. J. Biochem. 67, 247-256) was supplemented with dog pancreas microsomal membranes and used to investigate the synthesis and processing of presecretory proteins. Highly efficient processing and segregation of the major bovine pituitary secretory proteins was observed upon mRNA translation. In contrast to the wheat germ cell-free protein synthesizing system, there was no significant inhibition of translation in the reticulocyte lysate even in the presence of high concentrations of dog pancreas microsomal membranes. Since the latter are required for processing and segregation of presecretory proteins, these reactions could be driven to virtual completion in the reticulocyte lysate without affecting the overall rate of protein synthesis.