Two chromatographically separable forms of Escherichia coli elongation factor Tu.

Two forms of the elongation factor Tu from Escherichia coli have been separated by chromatography on DEAE-Sephadex A50. Obvious chromatographic artifacts have been ruled out by investigation of the elution profile of GDP (a component of the column buffer as well as a ligand of Tu) and by rechromatography of the two components, either separately to give the component peaks or together to give a double peak. The two components have been confirmed as Tu by the poly(uridylic)-dependent polyphenylalanine synthesis and by the distribution of the Tu protein as quantitated from sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Complexes with the elongation factors Ts and G have also been ruled out by activity profiles and by quantitation of the protein distribution, again on gels. The distribution of the two forms between ribosomal and supernatant fractions has been examined: one is bound preferentially to the ribosomal fraction and the other is found in the supernatant fraction. The possible significance of this is discussed.