Cloning and characterization of the Escherichia coli lit gene, which blocks bacteriophage T4 late gene expression.

Escherichia coli lit mutations inhibit gene expression late in infection by bacteriophage T4. We cloned the lit gene from wild-type E. coli and three independent lit mutants. We present evidence that lit mutations [renamed lit(Con) mutations] cause overproduction of the lit gene product and that overproduction of this product causes the inhibition of gene expression. We also present evidence that the lit gene product is nonessential for E. coli growth, although the gene is common to most E. coli K-12 strains.     

Modulation of stability of the Escherichia coli heat shock regulatory factor sigma.

The heat shock response of Escherichia coli is under the positive control of the sigma 32 protein (the product of the rpoH gene). We found that overproduction of the sigma 32 protein led to concomitant overproduction of the heat shock proteins, suggesting that the intracellular sigma 32 levels limit heat shock gene expression. In support of this idea, the intracellular half-life of the sigma 32 protein synthesized from a multicopy plasmid was found to be extremely short, e.g., less than 1 min at 37 and 42 degrees C. The half-life increased progressively with a decrease in temperature, reaching 15 min at 22 degrees C. Finally, conditions known previously to increase the rate of synthesis of the heat shock proteins, i.e., a mutation in the dnaK gene or expression of phage lambda early proteins, were shown to simultaneously result in a three- to fivefold increase in the half-life of sigma 32.     

Expression of the bacteriophage T4 denV structural gene in Escherichia coli.

The expression of the T4 denV gene, which previously had been cloned in plasmid constructs downstream of the bacteriophage lambda hybrid promoter-operator oLpR, was analyzed under a variety of growth parameters. Expression of the denV gene product, endonuclease V, was confirmed in DNA repair-deficient Escherichia coli (uvrA recA) by Western blot analyses and by enhancements of resistance to UV irradiation.     

Alterations in the cell envelope of Escherichia coli late in bacteriophage T4 infection

The cell envelope of Escherichia coli was examined for changes during late stages of bacteriophage T4 infection. Late events in T4 infection are shown to result in (i) a reduction in the effectiveness of membrane separation procedures employing either isopycnic sucrose gradient centrifugation or selective solubilization of inner membrane by detergent (Sarkosyl or Triton X-100), (ii) the appearance of a 54 000 dalton host protein in membrane preparations, (iii) the adventitious presence of detergent-resistant phage morphogenetic structures in membrane preparations, and (iv) a decrease in the activity of NADH oxidase and an apparent alteration in its association with inner membrane. These modifications occur regardless of the state of the $\text{e}$ and $\text{t}$ genes of T4.     

Cloned genes for bacteriophage T4 late functions are expressed in Escherichia coli

We have constructed derivatives of plasmid pMB9 carrying EcoRI digestion fragments of bacteriophage T4 DNA that code for late gene functions. When Escherichia coli strains carrying these plasmids are infected with T4 amber mutants, burst sizes up to 30% of the wild-type level are obtained. Single burst experiments imply that the phage progeny result from complementation and do not depend on marker rescue. By electrophoretic and immunological techniques, we have established that the cloned T4 late genes are transcribed and translated in uninfected cells. A serum blocking assay has been used to quantitate the levels of one of the T4 gene products, gp11, before and after T4 infection. Uninfected cells containing the cloned T4 gene 11 DNA have 0.1% and mini cells have 1% of the gp11 levels per unit protein found in cells late after T4 wild-type infection. There is little or no additional gp10 and gp11 formed from the cloned genes after T4 infection.     

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

Regulation of T4-specific mRNA synthesis was studied during leucine starvation of a leucine-requiring stringent Escherichia coli B strain. This was done by imposing starvation prior to T4 infection and then letting RNA synthesis proceed for different time periods. Rifampin or streptolydigin was added to stop further RNA synthesis, and protein synthesis was restored by addition of leucine. Samples were withdrawn at different times, and the enzyme-forming capacities found that, during conditions which elicit the stringent response in uninfected bacteria, immediate early mRNA is not stringently regulated. This conclusion contradicts the earlier conclusion of others, obtained by measuring incorporation of radioactive uracil; this is explained by the observation of Edlin and Neuhard (1967), confirmed and extended by us to the T4-infected cell, that the incorporation of uracil into RNA of a stringent strain is virtually blocked by amino acid starvation, whereas that of adenine continues at 30 to 50% of the rate seen in the presence of the required amino acid.     

Folate polyglutamates in T4D bacteriophage and T4D-infected Escherichia coli.

The folate compound which is a structural component of the Escherichia coli T-even bacteriophage baseplates, has been identified as the hexaglutamyl form of folic acid using a new chromatographic procedure (Baugh, C.M., Braverman, E. and Nair, M.G. (1974) Biochemistry 13, 4952-4957). It has also been found that the host cell contains a variety of polyglutamyl forms of folic acid. The major form is the triglutamate (about 50%) but small amounts of higher molecular weight folates including the octaglutamate (1.8%) have been identified. Upon infection with wild-type T4D bacteriophage there is a shift in the distribution of the folate compounds so that the folyl polyglutamyl compounds having the higher molecular weights are increased. Infection of E. coli with baseplate mutants of T4D containing an amber mutation in gene 28 resulted in the formation of significant amounts (over 7%) of folate compound(s) of molecular weight much higher than those observed either in uninfected cells or cells infected with wild-type T4D. It is suggested that the T4D gene 28 product functions to cleave glutamate residues from high molecular weight folyl polyglutamates to increase the availability of the folyl hexaglutamate for virus assembly.