TIF4631 AND TIF4632 - 2 YEAST GENES ENCODING THE HIGH-MOLECULAR-WEIGHT SUBUNITS OF THE CAP-BINDING PROTEIN COMPLEX (EUKARYOTIC INITIATION FACTOR-4F) CONTAIN AN RNA RECOGNITION MOTIF-LIKE SEQUENCE AND CARRY OUTAN ESSENTIAL FUNCTION

The 5' ends of eukaryotic mRNAs are blocked by a cap structure, m7Gppp X (where X is any nucleotide). The interaction of the cap structure wi th a cap-binding protein complex is required for efficient ribosome bi nding to the mRNA. In Saccharomyces cerevisiae, the cap-binding protei n complex is a heterodimer composed of two subunits with molecular mas ses of 24 (eIF-4E, CDC33) and 150 (p150) kDa. p150 is presumed to be t he yeast homolog of the p220 component of mammalian eIF-4F. In this re port, we describe the isolation of yeast gene TIF4631, which encodes p 150, and a closely related gene, TIF4632. TIF4631 and TIF4632 are 53% identical overall and 80% identical over a 320-amino-acid stretch in t heir carboxy-terminal halves. Bo proteins contain sequences resembling the RNA recognition motif and auxiliary domains that are characterist ic of a large family of RNA-binding proteins. tif4631-disrupted strain s exhibited a slow-growth, cold-sensitive phenotype, while disruption of TIF4632 failed to show any phenotype under the conditions assayed. Double gene disruption engendered lethality, suggesting that the two g enes are functionally homologous and demonstrating that at least one o f them is essential for viability. These data are consistent with a cr itical role for the high-molecular-weight subunit of putative yeast eI F-4F in translation. Sequence comparison of TIF4631, TIF4632, and the human eIF-4F p220 subunit revealed significant stretches of homology. We have thus cloned two yeast homologs of mammalian p220.