The role of cholesteryl 14‐methylhexadecanoate in the function of eukaryotic peptide elongation factor 1

Abstract

The binding of [3H]cholesteryl 14-methylhexadecanoate (CMH) by a highly purified peptide elongation factor 1 from rabbit reticulocytes is significantly enhanced by GTP and CTP, much less by guanosine 5''-[.beta.,.gamma.-methylene]triphosphate and not at all by ATP or UTP. Removal of endogenous CMH present in the molecule of the factor by digestion with immobilized cholesterol esterase resulted in an almost complete loss of GTPase activity and this could be restored to nearly normal values by the addition of the ester. The same holds true for the GTP-dependent autophosphorylation of the protein-synthesis factor. CMH was bound only by the .beta. subunit of the factor. Addition of the .alpha. subunit, which was inactive on its own, stimulated the binding of the ester to the .beta. subunit in a sigmoid dependance. The binding of the ester was significantly stimulated by aminoacyl-tRNA but this effect was fully abolished by NaF, indicating a relation of CMH to the dephosphorylation of the peptide elongation factor. Treatment of the factor with cholesterol esterase decreased its activity in the poly(U)-dependent binding of phenylalanyl-tRNA to ribosome and this activity was again restored by the addition of CMH. The ester thus interacts with the GTP-dependent autophosphorylation of peptide elongation factor 1 and in this way modulates the activity of the factor. A putative scheme is presented explaining the mode of action of CMH.