Protein phosphorylation and translation of messenger RNAs

Characterization of the poly(ADP-ribose) polymerase associated with free cytoplasmic mRNA-protein particles

Poly(ADP-ribose) polymerase associated with free cytoplasmic messenger ribonucleoprotein particles (mRNP) has been characterized in mouse plasmacytoma. This cytoplasmic enzyme undergoes auto-ADP-ribosylation and has a similar molecular weight and common antigenic sites with the chromatin bound poly(ADP-ribose) polymerase in spite of its DNA independency. The free mRNP poly(ADP-ribose) polymerase is released from the particle only by high saline concentrations (0.7 M KCl) and the dissociated enzyme expresses a higher activity. The treatment of free mRNP by RNase A stimulates the poly(ADP-ribose) polymerase activity. Partial destruction of mRNP by high saline concentration or mRNA digestion unmasks new protein sites for ADP-ribosylation. In view of the changes that occur in the free mRNP structure to permit mRNA translation, a possible role of poly(ADP-ribosylation) as an important post-synthetic modification of some of the mRNP proteins is discussed.

Insulin reduces HBsAg production by PLC/PRF/5 human hepatoma cell line. Brief report

Although its action at the molecular level is not completely understood, insulin, as well as its antagonist glucagon, certainly plays an important role in the modulation of protein synthesis. In order to observe whether insulin is involved in virus gene expression, we studied its effect on PLC/PRF/5 human hepatoma cell line, which posses HBV DNA sequences integrated at several sites. While human insulin had no effect on cell growth and increased the production of two plasma proteins, a selective inhibitory effect on HBsAg production could be detected. This observation might be useful for further studies both on virus gene expression and insulin action at the molecular level.