Interaction between lambda or phi80 prophage induction and gal operon expression

When Escherichia coli cells are cultivated with fucose on a rich medium giving rise to a strong catabolite repression, λh80 or φ80 prophage thermo-induction triggers a significant escape of the gal operon activity.     

A mutation defining ultrainduction of the Escherichia coli gal operon.

Tn10 insertion in the galS (ultrainduction factor) gene of Escherichia coli allows the gal operon to be constitutively expressed at a very high level, equal to that seen in a delta galR strain in the presence of an inducer. The insertion has been mapped by criss-cross Hfr matings and by marker rescue into Kohara phages at 46 min on the E. coli chromosome.     

Influence of the recF143 mutation of Escherichia coli K12 on prophage lambda induction.

Prophage lambda induction in a recF143 mutant of E. coli K12 was studied. The recF143 (lambda) lysogen was inducible by UV irradiation or treatment with mitomycin C. However, the time required for the onset of derepression brought about by these treatments was longer in the recF143 mutant than in rec+ strains, suggesting that the induction pathway was altered in the recF143 mutant. The recF143 (lambda) lysogen was induced at very low doses of UV irradiation or mitomycin C treatment. Moreover, the presence of the recF143 mutation increased the sensitivity to thermal induction of a tif strain.     

Influence of the recB21 mutation of Escherichia coli K12 on prophage lambda induction

The inactivation kinetics of the lambda repressor following bleomycin (BM), UV-irradiation and nalidixic acid (NAL) treatments were studied in the recB21 mutant of E. coli K12. The results showed essentially normal induction by UV-irradiation, delayed induction by BM and no induction by NAL. The results were compared with inactivation kinetics in lexA1 and recF143 mutants.     

Effect of transient lambda prophage induction on ultraviolet light resistance and recombination in Escherichia coli.

Transient induction of lambda prophage increases the ultraviolet light resistance of most exponentially growing Escherichia coli lysogens. Resistance is increased in wild-type, recB, recB recC, recB recC recF, and recB recC recL hosts. No enhancement in recA lysogens was found, nor was there enhancement in stationary cultures. Enhancement was dependent upon the lambdared recombination system. Transient induction also increases the genetic recombination rate in recB lysogens as measured in Hfr X F- matings.     

On the combined action of drugs on the lambda prophage induction in Escherichia coli K12 cells.

The capability of methotrexate, jododeoxyuridine and 5-fluorouracil to induce lambda prophage was compared when given alone or in combination. All these drugs were found to cause inducing conditions in Escherichia coli K12(lambda) cells. Combined action of jododeoxyuridine and methotrexate resulted in a pronounced increase in the number of free phages compared with that resulting the treatment either with methotrexate of jododeoxyuridine alone. Treatment with 5-fluorouracil caused inactivation of plaque forming ability in cells induced with methotrexate.     

Physical study of prophage excision and curing of lambda prophage from lysogenic Escherichia coli

A sex factor, F′450(λ), which can be isolated as a covalent circle of DNA, has been examined by alkaline sucrose gradient centrifugation of lysates of induced cells in order to study λ prophage excision. Thermal derepression of the prophage results in loss of F′450(λ) covalent circles, which is mediated by systems involved in excision and initiation of replication. When protocols known to result in prophage curing are used, the F′450(λ) is converted to an F′450 and a λ covalent circle; in normal excision leading to phage development, F′450 covalent circles are not found. We have shown that: (1) excision usually occurs later than initiation of DNA replication of the prophage so that the excised prophage is usually already replicated or in the act of replication; (2) the DNA growing points of the prophage leave the prophage and enter the bacterial DNA; (3) the int and xis genes are involved in the earliest detectable stage of the excision process, i.e. breakage of the DNA at the attachment region; (4) the xis gene product is involved in a weak non-specific nuclease activity in addition to its highly specific activity in excision; and (5) the excision system fails to attack a single attachment site.     

tif-dependent induction of colicin E1, prophage lambda, and filamentation in Escherichia coli K-12.

To help understand how the tif-1 mutation of the recA gene of Escherichia coli confers adenine activability on the recA protein, we used the fact that cytidine plus guanosine inhibits induction of prophage lambda and cell filamentation in a tif-1 mutant, and that adenine reverses this inhibition. We varied the amount of adenine in agar plates containing a fixed amount of cytidine and scored for survivors of three different tif-dependent lethal induction processes. Much more adenine was required for cell killing when cytidine was present than when it was absent. Therefore adenine does not override cytidine inhibition, but instead appears to compete with it for a site of action which may be on the recA protein. The competition is not at the cell transport level. Our results lead to a model in which the tif form of the recA protein is an allosteric enzyme that binds both negative and positive modulators. By varying the adenine-cytidine ratio of the medium it is possible to control the degree of induction in a tif-1 cell. For the three different tif-dependent inductions studied here, least adenine was required for lambda induction and most for lethal filamentation, presumably reflecting requirements for different amounts of activated recA protein in each process. Varying the adenine-cytidine ratio revealed two stable intermediate stages in lambda induction, as well as a stage of colicin E1 induction in which the cells produced colicin without cell death. The rate of filament formation could be similarly controlled. Experiments with tif (ColE1, lambda) gave evidence of a competition between colicin repressor and lambda repressor for activated recA protein.     

Effect of ozone on prophage induction in different strains of Escherichia coli K-12 lysogenic for lambda

Ozone was tested for its effect upon induction of lambda prophage in two different strains of Escherichia coli K-12. Based on the induction index and when compared to ultraviolet light, ozone appeared to be a weak, if any at all, inducer of the lytic cycle in E. coli. This is in agreement with other studies which have suggested that this agent is a weak inducer of the SOS functions.