Content of elongation factor Tu in Escherichia coli

The content of elongation factor Tu in E. coli B has been determined both by radioimmune assay and by GDP binding. The two assays gave comparable results: cells growing at 2 doublings per hour contained about 8 molecules of Tu per ribosome, whereas those growing at 0.22 doublings per hour contained about 14 molecules per ribosome. These levels resemble those reported for tRNA, in contrast with the 1:1 ratio of factor to ribosomes reported for elongation factors Ts and G.