Subcellular and regional distribution of casein kinase II and initiation factor 2 activities during rat brain development

The possible relationship between the subcellular and regional distribution of the activities of initiation factor 2 and casein kinase II, responsible for the phosphorylation of the beta subunit of the factor, has been studied during postnatal rat brain development. Both activities have been measured in four brain regions: diencephalon, hemispheres, cerebellum and brain stem, and in two subcellular fractions: postmicrosomal supernatant and the protein fraction associated with ribosomes, or crude initiation factors fraction. The specific activity of both the factor and the protein kinase is much higher in the protein fraction associated with ribosomes than in the soluble fraction and slightly higher in the hemispheres than in the other three regions. Changes in the activity of both proteins are in parallel with development, the activities increase in the postmicrosomal supernatant and decrease in the fraction associated with ribosomes from suckling (5-day-old) to adult (60-day-old) animals. The total activity of the factor and its kinase, calculated by summation of the activities of both subcellular fractions, does not change during development, and the distribution of activities between the two subcellular fractions observed during brain development, appears as an attractive regulation mechanism for the function of both proteins.