Effect of T4 infection on messenger RNA synthesis in Escherichia coli

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.

The activity of Escherichia coli DNA-dependent RNA polymerase on DNA templates of different origin. The effect of cAMP

DNA isolated from different T phages served as a better template for the synthetic activity of unmodified Escherichia coli RNA polymerase in the in vitro system than did the host DNA. cAMP significantly stimulated the activity of such a preparation of RNA polymerase. The stimulation was more pronounced with the host DNA template than with phage DNA. However, the synthetic activity of Escherichia coli RNA polymerase was greater in the presence of cAMP than without it when phage DNA served as the template.

Bacteriophage T4-induced shut-off of host-specific translation

To study the mechanism by which bacteriophage T4 inhibits the synthesis of inducible host enzymes we measured the formation of beta-galactosidase from preformed lac mRNA. Beta-Galactosidase was induced with isopropyl-beta-D-thiogalactopyranoside in the presence of 7-azatryptophan, a tryptophan analogue that is incorporated into proteins and renders the beta-galactosidase formed inactive. The accumulated las mRNA was measured by capacity to form active beta-galactosidase after a chase of the analogue with excess tryptophan. After T4 infection the ability to form beta-galactosidase from the preformed lac mRNA was rapidly lost even when T4 infection took place in the presence of rifampin. This restriction was dependent on the multiplicity of infection. At a multiplicity of infection of 8.6, 90% of the ability to express preformed lac mRNA was lost within 30 s. The kinetics of cessation of beta-galactosidase synthesis after T4 infection indicate that infection blocks initiation of lac mRNA translation.

Role of pyridine nucleotides in 5-fluorouracil-mediated reactivation of ultraviolet radiation damage

Ultraviolet irradiation (520 ergs/mm(2) at 254 nm) causes the respiration of Escherichia coli B/r cells to cease after about 90 min postirradiation incubation in a minimal medium containing glycerol as the sole source of carbon. The cessation of respiration is associated with loss of pyridine nucleotides. Agents which interfere with postirradiation transcription and translation prevent cessation of respiration. We have studied the effects of one of these agents, 5-fluorouracil (FU), on respiration, pyridine nucleotide levels, viability, capacity to support phage growth, and the repair of irradiated deoxyribonucleic acid (DNA). Addition of FU to cells immediately after irradiation results in the continuance of respiration at a linear rate and the maintenance of high levels of pyridine nucleotides. Cellular viability increases dramatically during the first 60 min of postirradiation incubation in the presence of FU. The ability of irradiated cells to support the growth of phage T4 is also greatly increased. FU treatment has no effect on the kinetics of pyrimidine dimer excision or the degradation of DNA. However, treated cells repair single-strand breaks resulting from early steps in excision repair slightly more efficiently than do untreated cells. The results support the hypothesis that one of the causes of death in these irradiated cells is the disappearance of pyridine nucleotides, coenzymes of certain respiratory dehydrogenases, and, in the case of nicotinamide adenine dinucleotide, for polynucleotide ligase, the enzyme responsible for the final step in the repair of DNA.

Inhibition of host protein synthesis during infection of Escherichi coli by bacteriophage T4. 3. Inhibition by ghosts

Deoxyribonucleic acid (DNA)-less T2 "ghosts" were prepared by osmotic shock and purified by KBr density gradient centrifugation. Escherichia coli B was treated with these ghosts in inorganic salts-glycerol medium to see which features of phage infection could be elicited by ghosts. At a multiplicity that was just sufficient to block induction of beta-galactosidase (EC 3.2.1.23), 89% of the bacteria were killed and the rates of ribonucleic acid (RNA) and DNA synthesis were about 10 to 15% of normal. However, protein synthesis was almost completely blocked but resumed after 30 min. During this period, it was possible to induce messenger RNA (mRNA) from the lactose operon, although this mRNA could not be translated into active beta-galactosidase. These results suggest to us that the viable cells surviving ghost infection synthesize nucleic acids at close to a normal rate but are temporarily blocked in protein synthesis. The continued formation of untranslated host mRNA mimics the pattern of bacterial synthesis just after whole-phage infection, and is consistent with the interpretation that the immediate block in the initiation of host translation by these viruses is due to their attachment.

Induction and repression of L-arabinose isomerase in bacteriophage-infected Salmonella typhimurium

The induction of l-arabinose isomerase in Salmonella typhimurium (LT2) is repressed on infection with clear plaque forming mutants (C(1) and C(2)) of the temperate phage P22 (C(+)). However, after infection with C(+) leading to lysogeny, there is a temporary repression. During this period, messenger ribonucleic acid (RNA) for l-arabinose isomerase accumulates. DNA-RNA hybridization data suggest that there is transcription of host DNA during the period of repression. Interference at the level of translation might be responsible for the cessation of induced enzyme synthesis.