Purification of histone messenger ribonucleoprotein particles from HeLa cell S-phase polysomes. Characterization of associated proteins.

We have purified HeLa histone mRNA from polysomes of S-phase cells which had been synchronized by hydroxyurea treatment. This mRNA was shown to direct the in vitro synthesis of all five histones which amount to at least 90-95% of its total translational activity. Polysomal histone mRNP was also purified and identified by cell-free translation and hybridization to a clone of histone DNA from E. esculentus. The protein moiety of this mRNP contained three prominent species of molecular weight 86,000, 73,000 and 53,000 daltons. The presence of the 73,000 species previously assessed to be bound to poly(A) is discussed in view of the fact that histone mRNA does not contain a pail. As globin mRNA, histone mRNA as well as histone mRNP were translated with equal efficiency in cell-free extracts from either S-phase or hydroxyurea blocked HeLa cells.