TRANSLATION of parathyroid hormone (PTH) mRNA in extracts of wheat germ1 or Krebs II ascites cells2 produces a polypeptide which contains the structure of PTH but which is larger than either PTH or its biosynthetic precursor proparathyroid hormone3,4 (proPTH). In the wheat germ system, this cell-free protein, designated pre-proparathyroid hormone (pre-proPTH) contains a methiomne at the amino terminus5 derived from initiator methionyl-tRNA6. Although this observation suggests that initiation of the synthesis of pre-proPTH is normal in the cell-free system, it is possible that in vitro initiation occurs at a codon that codes for an internal methionine in vivo. Such an artefact could be due to a degraded mRNA in which the in vivo initiator codon is lost or inactivated.
ASJC Scopus subject areas