CHARACTERIZATION OF YEAST TRANSLATION INITIATION-FACTOR 1A AND CLONING OF ITS ESSENTIAL GENE

Translation initiation factor eIF1A is required in vitro for maximal rates of protein synthesis in mammalian systems. It functions primarily by dissociating ribosomes and stabilizing 40 S preinitiation complexes. To better elucidate its precise role in promoting the translation initiation process, the yeast form of eIF1A has been identified in Saccharomyces cerevisiae and purified to homogenity on the basis of its cross-reaction with antibodies prepared against mammalian elF1A The apparent mass of yeast eIF1A (22 kDa) resembles that of the mammalian homolog (20 kDa), and the yeast factor is active in stimulating methionyl-puromycin synthesis in an assay composed of mammalian components. The gene encoding yeast eIF1A, named TIF11, was cloned and shown 60 be single copy. TIF11 encodes a protein comprising 153 amino acids (17.4 kDa); the deduced amino acid sequence exhibits 65% identity with the sequence of human eIF1A Both human and yeast eTF1A contain clusters of positive residues at the N terminus and negative residues at the C terminus. Deletion/disruption of TIF11 demonstrates that eIF1A is essential for cell growth. Expression of human eIF1A cDNA rescues the growth defect of TIF11-disrupted cells, indicating that the structure/function of yeast and mammalian eIF1A is highly conserved.