Purification and properties of a soluble factor required for the deoxyribonucleic acid-directed in vitro synthesis of beta-galactosidase.

The DNA-directed in vitro synthesis of beta-galactosidase has been investigated in a system dependent on Escherichia coli ribosomes, a salt wash of the ribosomes, and a supernatant fraction. Fractionation of the supernatant has made it possible to obtain dependencies on RNA polymerase and another protein factor for beta-galactosidase synthesis. The other factor (called L factor) cannot be replaced by a variety of proteins known to be required for transcription and translation. It has been purified to homogeneity and has a molecular weight of approximately 65,000. Although it is required for the in vitro synthesis of beta-galactosidase, it has no effect on total DNA-dependent amino acid incorporation under the conditions of the incubation. However, total RNA synthesis is depressed by the addition of L factor in a manner similar to what is observed with rho factor could not replace L factor in beta-galactosidase synthesis.