Isolation and in vitro translation of the messenger RNA coding for pancreatic amylase

RNA prepared from dog pancreas polysomes or microsomes directs the synthesis of pancreas-specific proteins in heterologous cell-free translation systems. A translation product, approximately 1500 daltons larger than authentic amylase, corresponding to pancreatic amylase was identified by immunoprecipitation with anti-amylase gamma-globulin and tryptic peptide analysis. We suggest that this larger form of amylase is an amylase precursor. Using amylase immunoprecipitation of reticulocyte translation reactions as an assay, we have shown that greater than 99% of the mRNA for amylase is associated with polysomes bound to the endoplasmic reticulum. Electrophoresis of pancreatic mRNA preparations in formamide-containing polyacrylamide gels and subsequent translation of the fractions have shown that amylase mRNA is of a discrete size with a mobility equivalent to that of 18 S ribosomal RNA, and therefore significantly larger than required to code solely for the amino acid sequence of the amylase precursor.