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Synthesis of S100 Protein on Free and Membrane‐Bound Polysomes of the Rabbit Brain
Author(s) -
Cosgrove James W.,
Heikkila John J.,
Marks Alexander,
Brown Ian R.
Publication year - 1983
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1983.tb08051.x
Subject(s) - polysome , rabbit (cipher) , chemistry , biochemistry , biophysics , neuroscience , microbiology and biotechnology , biology , ribosome , rna , computer science , gene , computer security
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 [ 35 S]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 SlOO 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.