Molecular Modifications Associated with Ageing of Globin Messenger RNA in vivo

Using polyacrylamide gel elution‐electrophoresis in aqueous medium, highly purified rabbit globin mRNA can be. fractionated into several populations of molecules differing by their mean poly(A) content. Both α and β globin mRNA are heterogeneous with respect to their electrophoretic mobilities. With the conditions used no separation of α and β globin mRNA occurs during electrophoresis. From the specific radioactivity distribution in the different mRNA fractions one can conclude that the polyadenylate sequence at the 3′ end of globin mRNA molecules becomes shorter with ageing. This shortening occurs on α, as well as β, globin mRNAs and the extent of heterogeneity in poly(A) content is similar for both globin mRNAs. Furthermore, using two different methods of mRNA fractionation (polyacrylamide gel elution‐electrophoresis and elution of poly(U)‐Sepharose‐bound mRNA at increasing temperatures) it is shown that old mRNA molecules differ from relatively young messages in their ability to direct cell‐free globin synthesis. Modifications reducing template activity in vitro thus seem to take place during globin mRNA ageing