In the preceding paper we described a procedure for the large-scale purification of the polypeptide elongation factors Tu-GDP, Ts, and Tu-Ts from E. coli. These three factors were purified to a homogeneous state as judged by several criteria,.and Tu-GDP and Tu-Ts were crystallized. Here we report some of the molecular and physicochemical characteristics of these factors, including molecular weight, amino acid composition, and absorption spectrum. The molecular weights of Tu-GDP, Ts, and native Tu-Ts, as determined by the Yphantis high-speed sedimentation equilibrium method, were 47,000, 34,000, and 66,000, respectively. Tu-Ts complex reconstituted from Tu-GDP and Ts had a molecular weight of 68,000. The molecular weights of Tu and Ts were also determined by SDS polyaery amide gel electrophoresis, and values of 47,000 and 36,000 were estimated for Tu-GDP and Ts, respectively. On the other hand, the Sephadex gel filtration of Tu-GDP, Ts, and Tu-Ts gave molecular weights of 48,000, 48,000, and 92,000, respectively. As described previously, the binding of [3H]GDP to Tu was one mole of GDP per 44,000 to 48,000g of protein. By a spectrophotometric procedure, the amount of GDP bound to Tu-GDP was estimated as one mole of GDP per 49, 000g of protein. It was concluded that both Tu and Ts contain no subunit structure, and that Tu-Ts was a complex consisting of one mole each of Tu and Ts. The amino acid compositions of Tu-GDP, Ts, and Tu-Ts were determined. Tu and Ts contained 3 and 2 residues of cysteine per mole of protein, respectively. Ts contained no tryptophan, and very little tyrosine. The amino acid composition of Tu-Ts was in good agreement with the values calculated from those of Tu and Ts, assuming the molar ratio of Tu and Ts in Tu-Ts complex as one. The absorption spectrum of Tu-GDP indicated the presence of bound GDP, while that of Ts showed no typical absorption peak at 280 mμ, as expected from its amino acid composition.