Binds to the 60S ribosomal subunit and prevents its association with the 40S ribosomal subunit to form the 80S initiation complex in the cytoplasm. Is also involved in ribosome biogenesis. Associates with pre-60S subunits in the nucleus and is involved in its nuclear export. Monomer. Associates with the 60S ribosomal subunit. Shuttles between cytoplasm and nucleus/nucleolus. Phosphorylation at Ser-174 and Ser-175 promotes nuclear export. Belongs to the eIF-6 family.