title: Synthesis of S100 protein on free and membrane-bound polysomes of the rabbit brain.
abstract: Free and membrane-bound polysomes were isolated from the cerebral hemispheres and cerebellum of the young adult rabbit. The two polysomal populations were translated in an mRNA-dependent cell-free system derived from rabbit reticulocytes. Analysis of the [35S]methionine-labeled translation products on two-dimensional polyacrylamide gels indicated an efficient separation of the two classes of brain polysomes. The relative synthesis of S100 protein by free and membrane-bound polysomes was determined by direct immuno-precipitation of the cell-free translation products in the presence of detergents to reduce nonspecific trapping. Synthesis of S100 protein was found to be twofold greater on membrane-bound polysomes compared with free polysomes isolated from either the cerebral hemispheres or the cerebellum. In addition, the proportion of poly-(A+)mRNA coding for S100 protein was also twofold greater in membrane-bound polysomes compared with free polysomes isolated from the cerebral hemispheres. These results indicate that the cytoplasmic S100 protein is synthesized predominantly on membrane-bound polysomes in the rabbit brain. We suggest that the nascent S100 polypeptide chain translation complex is attached to the rough endoplasmic reticulum by an ionic interaction involving a sequence of 13 basic amino acids in S100 protein.
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002474:Cell-Free System; D004591:Electrophoresis, Polyacrylamide Gel; D009419:Nerve Tissue Proteins / Q000096:biosynthesis*; D011061:Poly A / Q000032:analysis; D011132:Polyribosomes / Q000378:metabolism*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D009418:S100 Proteins / Q000096:biosynthesis*
chemical_list: D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D009418:S100 Proteins; D011061:Poly A