The structure and expression of the preproenkephalin gene

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Abstract
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 preproenkephal in mRNA encodes four copies of met-enkephalin, two copies of the met-enkephalin extended sequences and one copy of leuenkephalin; 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 hybridization probe to detect the corresponding mRNAs in rat adrenal grand 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.