Identification and quantitation of elongation factor EF-P in Escherichia coli cell-free extracts

EF-P, an elongation factor that stimulates peptide bond synthesis in vitro with some aminoacyl-tRNAs, has been identified by two-dimensional gel electrophoresis and the cellular content at three points in the growth curve has been measured. The molecular weight of EF-P is estimated to be 21 000. EF-P is a slightly acidic protein whose isoelectric point is close to RNA polymerase subunit alpha. The amount of EF-P present in Escherichia coli is about 1/10th that of EF-G and the level is independent of the stage of cell growth; there is about one EF-P per 10 ribosomes. It is also shown that a highly purified preparation of EF-P is free of all known protein synthesis factors and ribosomal proteins.