Pregrowth hormone: product of the translation in vitro of messenger RNA coding for growth hormone.

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Abstract
Membrane fraction RNA isolated from rat pituitary tumor (GC) cells was translated in a wheat germ extract. A product was synthesized which was immunologically related to growth hormone [GH], but which migrated more slowly than GH upon sodium dodecyl sulfate-acrylamide gel electrophoresis. The mobility of the cell-free product on gels of this type was unchanged by treatment with either KOH or RNase. The mobilities during paper electrophoresis of the methionine-containing tryptic peptides obtained from the cell-free product were identical to those obtained from GH synthesized and secreted by the GC cells. Molecular weights for GH and the cell-free product of 19,500 and 24,000, respectively, were determined by gel electrophoresis of these proteins together with marker proteins of known molecular weights. No protein with the properties of the cell-free product was detected after a 2 min incubation of the GC cells with [35S]methionine. Treatment of the GC cells with a protease inhibitor, L-1-tosylamide-2-phenyl-ethylchloromethyl ketone (TPCK), led to the appearance of a new polypeptide, innunologically related to GH, and with a mobility on gels identical to that of the cell-free product. The cell-free product may represent a GH precursor (pregrowth hormone) which is rapidly converted to GH in pituitary cells.