LOCALIZATION OF EUKARYOTIC INITIATION-FACTOR-2 IN NEURON PRIMARY CULTURES AND ESTABLISHED CELL-LINES

Eukaryotic initiation factor 2 (eIF-2) is a heterotrimeric protein wit h subunits alpha, beta and gamma that forms a ternary complex with Met -tRNA and GTP. It promotes the binding of Met-tRNA to ribosomes and co ntrols translational rates via phosphorylation/dephosphorylation mecha nisms. By means of immunofluorescence and post-embedding immunocytoche mistry of intact cells and quantitative immunoblotting of cell extract s, the cellular distribution of the initiation factor has been examine d in primary neuronal cultures as well as in two established cell line s: PC12 phaeochromocytoma cells and rat pituitary GH4C1 cells. Our res ults indicated that the initiation factor is located not only in the c ytoplasm but also in the nuclei of the cultured neurons and cell lines . In the cytoplasm, immunocytochemical studies reveal that the factor is present mainly in those areas that are rich in ribosomes. In the nu cleus, the immunolabelling of eukaryotic initiation factor 2 verified the presence of gold particles in both nucleolar and extranucleolar ar eas. The specific distribution of this factor on both sides of the nuc lear envelope suggests that it might have some nuclear-related functio n(s) besides its already known role in the control of translation.