Translation initiation factor eIF4G1 modulates the assembly of PET region in yeast ribosome biogenesis

eIF4G is an important eukaryotic translation initiation factor. In this study, eIF4G1, one of the eIF4G isoforms, was shown to join in 60S biogenesis directly. Mutation of eIF4G1 decreased the 60S ribosomal subunits significantly. The C-terminal fragment of eIF4G1 could complement the function in 60S biogenesis sufficiently. Analyses of its purified complex with mass spectrometry indicated that eIF4G1 was associated with the pre-60S directly. Strong genetic and direct protein-protein interactions were observed between eIF4G1 and Ssf1 protein. Upon deletion of eIF4G1, Ssf1, Rrp15, Rrp14, and Mak16 abnormally retained on the pre-60S complex. This prevented the loading of Arx1 and eL31 at the polypeptide exit tunnel (PET) site and the transition to a Nog2-complex. Our data indicate that eIF4G1 is important in facilitating PET maturation and 27S processing correctly.