Spermidine regulation of protein synthesis at the level of initiation complex formation of Met-tRNAi, mRNA and ribosomes.

Spermidine regulation of protein synthesis (stimulation at low concentrations and inhibition at high concentrations) was studied using a mRNA with a GC-rich 5'-untranslated region. It was found that the initiation complex formation of mRNA, Met-tRNAi, and 40 S ribosomal subunits was regulated by spermidine. The inhibition of initiation complex formation at high spermidine concentrations was greater with 80 S ribosomes than with 40S ribosomal subunits. This was partially explained by the spermidine inhibition of initiation factor-dependent RNA helicase activity.