Changes in the activity and distribution of the ribosomal dissociation factor of rat liver during growth

In order to assess the relationships between the rate of growth and the activity of the initiation factors of protein synthesis, the activity and intracellular distribution of partially purified preparations of the ribosomal dissociation factor, obtained from the 0.5 M KCl wash of the ribosomes and from the high-speed supernatant (cytosol) of rat liver, were investigated in animals aged 1, 30, 60, 90 and 180 days. During the early phases of growth the activity of the dissociation factor was found mostly in the KCl wash of ribosomes. With advancing age, this activity decreased whereas that of the supernatant was found to increase. The activity of the supernatant was similar to that of ribosomes at 60, 90 and 180 days of age. The older rats showed, however, a decline in the activity of the dissociation factor. These observations suggest an increased rate of protein synthesis initiation in the early phases of growth in rat liver. With advancing age, a progressive reduction of ribosome recycling into subunits might take place, due to the increased accumulation of the dissociation factor in the cytosol. This might suggest a lowering of the initiation reactions of protein synthesis in such conditions.