What is the mechanism by which initiation factor eIF4GI, and its paralogue, p97 (DAP5), selectively promote translation of different subsets of mRNAs?. (360G-Wellcome-087729_Z_08_Z)

We have previously proposed that resumption of scanning and reinitiation following translation of a short uORF requires that the eIF4G/eIF3/40S subunit interactions (which were instrumental in promoting initiation at the uORF AUG) persist throughout the time taken for uORF translation; and that, by implication, the canonical initiation factors are sufficient, with no additional protein factor(s) required specifically for rescanning/reinitiation. We will use the defined in vitro system, consistin g of purified initiation, elongation and termination factors, defined aminoacyl-tRNAs, and ribosomal subunits to test these two propositions. In addition, working with this purified system and also unfractionated reticulocyte lysate (RRL) we will use formaldehyde fixation and sucrose gradient centrifugation to test directly for short-term persistence of the eIF4G/eIF3/ribosome interactions following 80S initiation complex formation. For p97, a priority will be to identify targets of p97 action (by using micro-array analysis of polysomal mRNA from cells in which p97 has been silenced). This will allow the design of appropriate dedicated reporters. The effects of recombinant p97, and its caspase cleavage product, p86, on translation of these dedicated reporters (compared with standard reporters) will then be studied in RRL or HeLa cell extracts, eIF4G-depleted versions of these systems, and the fractionated system.