Organization of Vitellogenin Polysomes, Size of the mRNA and Polyadenylate Fragment

Abstract

A heavy polysome fraction containing vitellogenin mRNA was isolated from the liver of oestradiol-treated chicks. As determined by urea – polyacrylamide gel electrophoresis, the molecular weight of vitellogenin mRNA is about 2.5 × 10⁶. The mRNA contains a polyadenylate segment of about 220 nucleotides at the 3′ end. The remaining 7000 nucleotides are sufficient to code for a polypeptide of M_r about 270000. Combining ‘run off’ experiments of heavy polysomes in vitro together with radioimmunoprecipitation and polyacrylamide gel electrophoresis of the translation product, we concluded that vitellogenin mRNA is probably monocistronic and the 2.5 × 10⁶−M_r mRNA codes for two polypeptides, M_r 30000 and 240000. The largest polypeptide is, in our cellfree system and liver homogenate, readily cleaved into smaller peptides.