DNA-Directed Synthesis in vitro of β -galactosidase: Requirement for a Ribosome Release Factor

The DNA-directed synthesis of β -galactosidase in Escherichia coli extracts has been investigated in a partially fractionated system. A dependency was obtained for 3′,5′-cyclic AMP receptor protein and also for a factor, from the salt wash of ribosomes, that has been purified to near homogeneity. This factor has been identified with a ribosome release factor previously purified from the supernatant fraction by A. Hirashima and A. Kaji [(1972) Biochemistry 11, 4037-4044]. In the coupled transcription-translation system this factor stimulates β -galactosidase synthesis and total protein synthesis 2- to 4-fold. It is thus clear that the ribosome release factor has a physiological function in translation. It may also affect transcription, because it stimulated total RNA synthesis up to 50% in this in vitro system.