Initiation factor requirements for the in vitro synthesis of T4 lysozyme

François Gros: from antibiotics to messenger RNA

François Gros was a prominent French Molecular Biologist who made a major contribution to the discovery of messenger RNA in 1961. He pursued outstanding research on bacterial mRNA and its translation into proteins followed by pioneering work on muscle differentiation. I was lucky to be among his graduate students and owe much of my success in science to him. In this short text I will describe how the initial post-war studies of François guided him to discover the existence of short-lived RNA in bacteria, the messenger RNA containing the information for protein synthesis. I will also recount the influence he had on his students and their carrier in science.

Translation of MS2 RNA in vitro in the absence of initiation factor IF-3

An Escherichia coli cell-free translational system, deprived of initiation factor IF-3, has been used to study the role of the factor in protein synthesis. In this system, 30-S ribosomal subunits are preincubated together with MS2 phage RNA in a small volume in the presence of 10 mM Mg(Ac)2; the missing components required for protein synthesis are then added and assembly of elongating ribosomes is allowed to occur. This stepwise assembly process permits formation of functional complexes which can carry out protein synthesis in the complete absence of IF-3. The translational products, obtained in the absence of IF-3, have been analysed and shown to be similar to those synthesized in the presence of the factor. The main product observed is the phage coat protein.

Increased translation as a result of elevated initation factor activity after administration of 3-methylcholanthrene

Protein synthesis initiation factors present in a crude 0.5 M KCL microsomal wash fraction were isolated from the livers of immature rats that had been injected either 2 or 17 hours earlier with the plycyclic hydrocarbon, 3-methylcholanthrene (3MC), and then were tested for their ability to stimulate natural mRNA-directed protein synthesis in vitro. After purification of the initiation factors by means of ammonium sulfate fractionation, and DEAE-cellulose and Sephadex G-200 chromatography, M2A and M2B, but not M3 or M1, from the livers of 3MC-pretreated rats were more active than were similarly-prepared control factors in their ability to initiate the synthesis of rabbit globin polypeptides in a highly fractionated cell-free protein synthesizing system derived from rabbit reticulocytes. The greater activity of the M2A and M2B preparations from drug-treated rat liver did not appear to be due to differences in the composition of initiation factor protein extracted from the livers of control or experimental rats and occurred very early after administration of 3MC, i.e., 2 hr. The role of the protein synthesis initiation factors in the altered rates of protein synthesis which accompany cytodifferentiation and growth is discussed.