IDENTIFICATION OF PARTNERS OF TIF34, A COMPONENT OF THE YEAST EIF3 COMPLEX, REQUIRED FOR CELL-PROLIFERATION AND TRANSLATION INITIATION

Eukaryotic initiation factor-3 (eIF3) in the yeast Saccharomyces cerev isiae plays a central role in initiation of translation. The eIF3 comp lex contains at least eight different proteins, but, as yet, little is known about the function of the individual proteins. In this study we have characterized the role of TIF34 (eIF3-p39), a recently identifie d WD-40 domain-containing protein of 39 kDa, in the eIF3 complex, Usin g temperature-sensitive mutants of TIF34 we show that this protein is required for cell cycle progression and for mating and plays an essent ial role in initiation of protein synthesis. By two-hybrid screening w e have identified two partners that directly associate with TIF34: PRT 1, a previously characterized eIF3 subunit, and a novel protein of 33 kDa (eIF3-p33) which is part of the eIF3 complex and has an RNA bindin g domain. TIF34 and p33 interact with each other and overexpression of p33 complements the growth defect of a tif34-ts mutant, Our results p rovide support for both physical and functional interactions between t hree subunits, TIF34, PRT1 and p33, in the eIF3 complex.