Mitochondrial Poypeptide Elongation Factor EF-Tu of Saccharomyces cerevisiae. Functional and Structural Homologies to Escherichia coli EF-Tu

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Abstract
The polypeptide elongation factor EF-Tu was isolated from a mitochondrial 100,000 .times. g supernatant of the yeast Saccharomyces cerevisiae and purified over 880-fold by DEAE-Sephadex chromatography and gel filtration. The factor efficiently replaces bacterial EF-Tu in a phenylalanine polymerizing cell-free system of Escherichia coli, it binds GDP and it protects phenylalanyl-tRNA against hydrolysis of the ester bond in the presence of 10 mM GTP. The polymerizing activity of the mitochondrial factor is inhibited to 90% by 50 .mu.M N-ethylmaleimide and to 50% by 2.5 .mu.M kirromycin. The purified factor contains 2 major polypeptides of apparent MW 48,000 and 34,000. Antibodies raised against the 48,000-MW protein react with E. coli EF-Tu, as revealed by immune blotting and by the inhibition of phenylalanine polymerization. No reaction was observed between anti-(34,000-MW and 48,000-MW) protein or E. coli EF-Tu. The 48,000-MW protein has the same isoelectric point (pI = 6.2) and a content of cysteine and basic amino acids similar to the bacterial EF-Tu. The 48,000-MW protein is probably the analog to E. coli EF-Tu, and yeast mitochondrial EF-Tu is functionally and structurally more related to bacterial EF-Tu than cytosolic EF-1 of the same cell.