Developmental studies of the first step of the initiation of brain protein synthesis, role for initiation factor 2

Developmental changes at the level of initiation step of translation in the rat brain were studied. The level of deacylated tRNAimet in rat brain was measured at two stages of postnatal development. Although the amount of tRNA was slightly lower in adult than in young (4 day old) rats, the charging capacity of initiator tRNAimet in vitro was similar at both ages. No differences during development were found in methionyl-tRNA synthetase activity, which throws doubt on its possible participation in regulation of the initiation step. When assayed in the ribosomal salt wash protein fractions, initiation factor 2 activity decreased during brain development, and increased activities were detected in the supernatant of the microsomal fractions. The decrease in eIF-2 activity paralleled the observed decrease in the rat of overall protein synthesis or initiation activity in vitro, suggesting that the regulation of the initiation step of translation during brain development may be tightly linked to changes in initiation factor 2 activity in brain tissue.