Cell-free synthesis of porcine proopiomelanocortin: two distinct primary translation products

Polyadenylated RNA prepared from porcine pituitary intermediate lobes was translated in the cell-free rabbit reticulocyte system. Two translation products with apparent relative masses (Mrs) of 37 500 and 35 000 on polyacrylamide – sodium dodecyl sulfate gel electrophoresis were immunoprecipitated with a β-melanophore-stimulating hormone (β-MSH) antiserum. Tryptic digestions after citraconylation of the lysine residues and purification of the peptides by high performance liquid chromatography demonstrated that both polypeptides contained authentic β-endorphin sequences. N-terminus microsequencing of the translation products labeled with [3H]leucine revealed the following partial amino acid sequence for the polypeptides with Mrs of 37 500 and 35 000: Leu8, 11, 12, 13, 15,16, 17, 20, 28, and 36 and Leu 3, 11, 12, 13, 15, 16, 17, 28, and 36, respectively. These results taken together prove the existence of two distinct mRNAs coding for proopiomelanocortin in the porcine pituitary intermediate lobe.