Mechanism of action of the wheat germ ribosome dissociation factor: Interaction with the 60 S subunit

Recently a ribosome dissociation factor that stimulates natural mRNA translation has been isolated from extracts of wheat germ. In this investigation, we have studied the subunit site of action of the purified ribosome dissociation factor (eucaryotic initiation), eIF-6. The following evidence strongly indicates that eIF-6 acts as a dissociation factor by binding to the 60 S ribosomal subunit and preventing its interaction with the 40 S subunit. Incubation of 60 S subunits with eIF-6 reduces the formation of 80 S monosomes when 40 S subunits are subsequently added at 5 mm Mg²⁺. The 40 S subunits preincubated with eIF-6 reassociate normally with 60 S subunits. ¹⁴C-labeled eIF-6 binds to 60 S subunits but not to 40 S subunits. Slight binding to 80 S ribosomes is also observed. The interaction of eIF-6 with the 60 S subunit requires an elevated temperature, and occurs rapidly at 37 °C.