Functional analysis of the TIF32-HLD-PRT1-RRM-HCR1 module of the yeast translation initiation factor 3

Abstract

The eIF3 is in yeast S. cerevisiae composed of five core essential subunits (TIF32, NIP1, PRT1, TIF34 and TIF35) and one nonessential substoichiometric subunit (HCR1), and as such represents the most complex initiation factor among all. Perhaps owing to that, it was shown to stimulate nearly all steps of the initiation pathway culminating in the formation of the 80S initiation complex at the AUG start codon on mRNA. Yeast eIF3 was also demonstrated to assemble together with the ternary complex, eIF1 and eIF5 into so called Multifactor complex that can exist free of ribosomes and whose formation greatly stimulates initiation efficiency. TIF32, the largest eIF3 subunit, was shown to make at least two critical contacts with the 40S ribosomal subunit and its middle domain, designated as the HLD, to share a significant sequence similarity with the HCR1 subunit. Experiments conducted here indicate that the TIF32-HLD and HCR1 share also some functional similarity as the recombinant HLD expressed under control of the HCR1 promoter in a domain- swapping experiment partially suppressed the slow growth phenotype of cells deleted for HCR1. In addition to the HLD, HCR1 also simultaneously interacts with the RRM domain of PRT1, which is considered to be the main scaffolding subunit of eIF3. The group of Dr. P.J....