[Distribution of elongation factors EF-1 and EF-2 among components of rabbit reticulocyte lysate]

The distribution of activity of the elongation factors EF-1 and EF-2 among the components of rabbit reticulocyte lysate separated by sucrose density gradient centrifugation was studied. At low ionic strength (0.01 M KCl) about 30% of the EF-1 activity was found in polyribosomes. At moderate ionic strength (0.1 M KCl) the EF-1 activity was absent in the polyribosomes. An addition of RNA excess to the lysate prior to centrifugation at low ionic strength resulted in elimination of the EF-1 activity from the polyribosomes. This indicates that EF-1 is reversibly bound to the polyribosomes and that EF-1 may be retained on them due to interaction with RNA of polysomes mediated by its RNA-binding site. After dissociation of polyribosomes containing EF-1 in the presence of EDTA and subsequent fractionation of the dissociation products at low ionic strength (0.01 M KCl) the EF-1 activity was revealed in the ribosomal subparticles (predominantly in 60S). At 0.1 M KCl EF-1 mainly sedimented in the zone of distribution of polyribosomal informosomes. The elongation factor EF-2 was not revealed in polyribosomes during lysate centrifugation even at low ionic strength which corresponds to its lower affinity for RNA.