Translational active mRNPs from rabbit reticulocytes are qualitatively different from free mRNA in their translatability in cell-free system.

The translatability of polyribosomal and free mRNPs from rabbit reticulocytes and their mRNA was compared. Both classes of mRNPs turned out to be active in rabbit reticulocyte lysates. Considerable differences between mRNPs and mRNA have been revealed. The most striking feature of mRNPs was that high concentrations of mRNPs do not inhibit protein biosynthesis, whereas high concentrations of mRNA strongly inhibit this process. This inhibition is specific for mRNA and does not occur at the addition of the same amount of rRNA from E. coli. The features of mRNP translation are not the result of addition of the supplementary translation factors within particles. The specific function of mRNP proteins in the process of translation is under discussion.