Cell-free translation of proline-rich protein mRNAS from human submandibular gland.

RNA was isolated from a human submandibular gland and separated into poly A-enriched and poly A-deficient fractions by chromatography on oligo (dT) cellulose. Both of these RNA fractions stimulated methionine incorporation into polypeptides in a reticulocyte lysate translation system. Two in vitro translation products templated by poly A-enriched mRNA were isolated by immunoprecipitation with immune serum directed against human salivary anionic proline-rich protein I. These polypeptides were shown to be precursors of proline-rich proteins on the basis of Mr, affinity for the antiserum, and preferential incorporation of proline. This study is the first to demonstrate cell-free translation of the mRNAs for human proline-rich salivary protein precursors.