Pre-Proparathyroid Hormone: A Direct Translation Product of Parathyroid Messenger RNA

An 8-15S RNA fraction from calf parathyroid glands stimulated the incorporation of radioactive lysine and methionine into protein by 15- to 30-fold in a wheat germ extract. The major product, representing 25% of the total protein synthesized, could be bound to an antiserum to parathyroid hormone and binding was inhibited by parathyroid hormone. The chromatographic mobilities of the two tryptic peptides of the cell-free product that contained methionine were identical to the corresponding peptides of parathyroid hormone. Upon electrophoresis in acidic or sodium dodecyl sulfate-acrylamide gels, the cell-free product migrated more slowly than either parathyroid hormone or its biosynthetic precursor, proparathyroid hormone. Analysis of cyanogen bromide products indicated that the cell-free product contained an additional sequence of amino acids at the amino-terminal end. A protein corresponding to the cell-free product could not be detected in intact cells even during incubations with [³H]leucine as short as 2 min, which suggests the protein may be a transient precursor to proparathyroid hormone.