CHARACTERIZATION OF BRAIN RIBONUCLEOPROTEIN-PARTICLES

Abstract— Brain RNP particles were characterized to determine whether they play a role in the regulation of brain protein synthesis. RNP particles were isolated from the postribosomal supernatant of cerebral hemispheres of young rabbits, employing conditions which minimize adventitious protein‐RNA interactions. Brain RNP particles consist of a different set of proteins compared to proteins associated with either 40 and 60s ribosomal subunits or polysomal mRNA. Poly(A+)mRNA from brain RNP particles stimulates the incorporation of [35S]methionine in a wheat embryo cell‐free system and codes for a different set of proteins compared to poly(A+)mRNA isolated from polysomes (with some overlap; i.e. mRNA coding for brain‐specific S100 protein is present in both RNP particles and polysomes). Addition of total brain RNP particles to a cell‐free wheat embryo system inhibits the endogenous incorporation of [35S]methionine. Total RNP particles were fractionated by sucrose density gradient centrifugation into a‘light’and a‘heavy’fraction. The light RNP fraction inhibited while the heavy RNP fraction stimulated protein synthesis in the wheat embryo cell‐free system. Analysis of the protein composition of fractionated RNP particles revealed that the light and heavy RNP particles contained different sets of proteins. Together these results suggested that one class of brain RNP particles may contain a translational inhibitor and may be involved in the regulation of protein synthesis in the brain. Copyright © 1979, Wiley Blackwell. All rights reserved