Induction of rat liver metallothionein mRNA and its distribution between free and membrane-bound polyribosomes

Publisher Website
Google Scholar
Abstract
Total membrane-bound and free polyribosomes were purified from livers of Zn2+-treated and control rats. Polyadenylated RNA was separated from the polyribosomal RNA extracts by oligo(dT)-cellulose chromatography and translated in a wheat-germ cell-free translation system. Newly synthesized 35S-labeled metallothionein was isolated from the other [35S]methionine-labeled translation products by activated-thiol-Sepharose 4B chromatography. The purity of the 35S-labeled metallothionein product was substantiated by sodium dodecyl sulfate/polyacrylamide-gel electrophoresis. Zn administration resulted in an elevation of metallothionein mRNA activity to 11% of the total polyribosomal mRNA activity. The vast majority of biologically active metallothionein mRNA was localized in the free polyribosomal pool, at least 94% and 97% in control and Zn-treated rats, respectively. The increase in the percentage of polyribosomal mRNA coding for metallothionein after Zn administration was 3-fold, whether measured directly in total polyribosomal mRNA or as a combination derived from membrane-bound and free polyribosomal mRNA. The induction of metallothionein mRNA by Zn apparently involves only free polyribosomes. The function of metallothionein may be limited to intracellular processes.