A GOLGI LOCALIZATION SIGNAL IDENTIFIED IN THE MENKES RECOMBINANT PROTEIN

Menkes disease arises from a genetic impairment in copper transport. T he gene responsible for the phenotype has been identified as a copper transporting ATPase (ATP7A), Recently, the protein encoded by the ATP7 A gene has been localized to the Golgi complex, In order to investigat e the role of the Menkes disease protein in copper transport, recombin ant constructs containing both the full-length open reading frame and an alternatively spliced form have been successfully expressed and loc alized in mammalian cells. Other studies of a patient with occipital h orn syndrome, an allelic variant of Menkes disease, have demonstrated that only this alternatively spliced isoform and not the full-length f orm is expressed in this patient. The milder form of this patient's ph enotype suggests that the alternatively spliced isoform has some funct ional role in copper transport. In the present study the full-length r ecombinant Menkes protein was shown by immunofluorescence to localize to the Golgi apparatus and the alternatively spliced form, lacking seq uences for transmembrane domains 3 and 4 encoded by exon 10, was shown to localize to the endoplasmic reticulum, Using sequences from exon 1 0 fused to a non-Golgi reporter molecule, a 38 amino acid sequence con taining transmembrane domain 3 of the Menkes protein was found to be s ufficient for localization to the Golgi complex. Therefore, the protei n sequence encoded by exon 10 may be responsible for this differential localization and both isoforms may be required for comprehensive tran sport of copper within the cell.