Translation of messenger ribonucleic acid from isolated pancreatic islets and human insulinomas

RNA preparations from isolated rat pancreatic islets and from human insulinomas were injected into oocytes of Xenopus laevis which were then incubated with [3H]leucine. Acid-ethanol extracts of the oocytes were immunoprecipitated with anti-insulin serum using the double antibody technique. Sodium dodecyl sulfate disc gel electrophoresis of the immunoprecipitates showed the presence of an insulin-displaceable immunoreactive material with a molecular weight of about 18,000 in extracts from oocytes injected with RNA of 9-11 S. This immunoreactive product was not detected in extracts from oocytes injected with buffer or 4-8S RNA or RNA heavier than 11 S. These observations suggest the involvement of a precursor larger than proinsulin in the biosynthesis of insulin.