The structure and expression of the preproenkephalin gene

Enkephalins are pentapeptides with opioid activity which are found in a wide variety of tissues. Studies of enkephalin-containing peptides from the adrenal gland have established that the mature pentapeptides are derived by proteolytic processing of a precursor protein. We have shown that human adrenal medullary tumours contain mRNA which can be translated in vitro to yield a single major enkephalin precursor. The sequence of cloned cDNA shows that the preproenkephalin mRNA encodes four copies of met-enkephalin, two copies of met-enkephalin extended sequences and one copy of leu-enkephalin; each copy is flanked by paired basic amino acids which are presumably recognised by the processing protease. We have used the cloned human cDNA as a hybridisation probe to detect the corresponding mRNAs in rat adrenal gland and, in smaller amounts, in rat brain. We have been unable to detect in brain any other cross-hybridising mRNAs which might encode other putative precursor proteins.