Regulation of early mRNA synthesis after bacteriophage T4 infection of Escherichia coli

Expression and DNA sequence of the cloned bacteriophage T4 dCMP hydroxymethylase gene

A plasmid expressing the cloned bacteriophage T4 gene 42 gave the same levels of complementation of gene 42 mutants in a polarity-suppressing rho mutant as in a rho+ host. A reading frame likely corresponding to gene 42 and putative promoter and terminator sequences were identified in the partial sequence of the cloned fragment.

Induction of the heat shock regulon of Escherichia coli markedly increases production of bacterial viruses at high temperatures

Production of bacteriophages T2, T4, and T6 at 42.8 to 44 degrees C was increased from 8- to 260-fold by adapting the Escherichia coli host (grown at 30 degrees C) to growth at the high temperature for 8 min before infection; this increase was abolished if the host htpR (rpoH) gene was inactive. Others have shown that the htpR protein increases or activates the synthesis of at least 17 E. coli heat shock proteins upon raising the growth temperature above a certain level. At 43.8 to 44 degrees C in T4-infected, unadapted cells, the rates of RNA, DNA, and protein synthesis were about 100, 70, and 70%, respectively, of those in T4-infected, adapted cells. Production of the major processed capsid protein, gp23, was reduced significantly more than that of most other T4 proteins in unadapted cells relative to adapted cells. Only 4.6% of the T4 DNA made in unadapted cells was resistant to micrococcal nuclease, versus 50% in adapted cells. Thus, defective maturation of T4 heads appears to explain the failure of phage production in unadapted cells. Overproduction of the heat shock protein GroEL from plasmids restored T4 production in unadapted cells to about 50% of that seen in adapted cells. T4-infected, adapted E. coli B at around 44 degrees C exhibited a partial tryptophan deficiency; this correlated with reduced uptake of uracil that is probably caused by partial induction of stringency. Production of bacteriophage T7 at 44 degrees C was increased two- to fourfold by adapting the host to 44 degrees C before infection; evidence against involvement of the htpR (rpoH) gene is presented. This work and recent work with bacteriophage lambda (C. Waghorne and C.R. Fuerst, Virology 141:51-64, 1985) appear to represent the first demonstrations for any virus that expression of the heat shock regulon of a host is necessary for virus production at high temperature.

Isolation of Escherichia coli mutants with changed regulation of uracil uptake

The incorporation of uracil into the pyrimidine ribonucleotide pools of Escherichia coli is strongly restricted under stringent conditions. Previously, we have suggested that this inhibition can be explained by the allosteric properties of uracil phosphoribosyltransferase. It has been proposed that this enzyme performs the uptake of uracil into the cell by transporting it across the cytoplasmic membrane, with the stimultaenous formation of UMP. To test this hypothesis it would be helpful to have mutants with changed regulation of uracil uptake, and in the present work, a method is introduced for the selection of such mutants. This method is based on phenotypic suppression of amber mutations by 5-fluorouracil (5FU). Mutants were isolated in an arginine-requiring strain of E. coli carrying an amber mutation in argI, the ornithine transcarbamylase gene. To facilitate the phenotypic rescue of this defective gene, mutants which overproduced ornithine transcarbamylase mRNA were isolated as a first step. The absence of exogenously added arginine causes stringent conditions, and phenotypic rescue by 5FU is, thus, prevented, unless the 5FU uptake mechanism is mutationally changed in such a manner that the drug is taken up into the cell. Three mutants in which the growth could be supported by 5FU in the absence of arginine were isolated. Two of them had acquired an increased ability to take up uracil under stringent conditions.

Evidence for a diffusible T4 bacteriophage protein governing the initiation of delayed early RNA synthesis

Two forms of prereplicative phage RNA can be discerned in Escherichia coli early after infection with bacteriophage T4, immediate early and delayed early RNA. The transition from immediate early to delayed early RNA synthesis is inhibited by chloramphenicol. The present work presents evidence for the existence of a phage-specific protein, which effects this transition. Delayed early RNA formation was measured by a cistron-specific enzyme-forming-capacity method, in which RNA synthesized in the presence of chloramphenicol was allowed to express itself into enzyme activity after (i) the addition of rifampin to inhibit further transcription and (ii) subsequent removal of chloramphenicol. As representatives of delayed early transcription, the two phage-specific enzymes dCTPase and deoxynucleotide kinase were chosen. Primary infection with a phage mutant defective in one of these two enzymes was found to induce a diffusible factor, which in the presence of chloramphenicol could effect the formation of delayed early RNA corresponding to the missing enzyme, upon superinfection with wild-type phage. The activity of this factor, acting in trans, was abolished by the amino acid analogue ethionine. Mutation in the suA gene of the host did not relieve phage of the apparent need for protein synthesis in the transition from immediate early to delayed early phage RNA synthesis.