NUCLEASE ACTIVITY IN DEFECTIVE LYSOGENS OF PHAGE MU. II. A HYPERACTIVE MUTANT

Isolation of suppressor sensitive mutants in the Ai gene of phage lambda

Previous experiments have shown that mutations in the Ai gene can suppress the growth defect of lambda N- phages. Many temperature resistant derivatives of phage lambdatsN9 have been isolated and among these 5 have been found which are Ai- and have an amber suppressible behaviour. These mutants can help in defining the role of the Ai gene in phage lambda development.

Purification and properties of the gamma-protein specified by bacteriophage lambda: an inhibitor of the host RecBC recombination enzyme

Previous experiments have indicated that the gam gene of bacteriophage lambda is responsible for an inhibition of the RecBC DNase-an enzyme that is essential for the major host pathway of genetic recombination. We report here experiments that define the inhibitor as the protein product of the gam gene ("gamma-protein") and that characterize the inhibition reaction with highly purified preparations of gamma-protein and RecBC DNase. Genetic characterization was performed with partially purified fractions prepared from cells infected with various lambda mutants. An activity that inhibits RecBC DNase was absent in extracts prepared after infection by phage that carry nonsense or deletion mutations in the gam gene; this activity was highly thermolabile in an extract prepared after infection by phage that carry a temperature-sensitive mutation in the gam gene. For biochemical characterization, the gamma-protein has been purified more than 800-fold. This highly purified preparation inhibited all of the known catalytic activities associated with the RecBC enzyme, but exhibited no detectable DNase or ATPase activities by itself. These findings are discussed in terms of their implications for regulation of genetic recombination and bacteriophage lambda development.

Regulation of the expression of the N gene of bacteriophage lambda

A quantitative assay for the N protein of bacteriophage lambda has been used to study the in vivo regulation of N gene expression. The assay makes use of the observation that in a cell-free protein-synthesizing system from Escherichia coli programmed with lambdaN(-) DNA the lambda endolysin is made only if N protein is added to the reaction. The rate of synthesis of N protein in vivo is negatively controlled by the products of the CI and tof genes of the phage. Furthermore, N protein activity is extremely unstable in vivo. During normal cell growth at 35 degrees , the half-life of N protein is about 2 min.

Regulation of repressor expression in lambda

A new gene in bacteriophage lambda is described. The product of this gene cro prevents expression of immunity and regulates the expression of those genes to the left of the immunity region. cro(-) mutants have been isolated and characterized.

The role of the N gene of phage lambda in the synthesis of two phage-specific proteins

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Deoxyribonucleic acid replication in lambda bacteriophage mutants

After ultraviolet light induction of Escherichia coli K-12 strain W3350(lambda), several structural intermediate forms of phage deoxyribonucleic acid (DNA) are synthesized. The early defective lysogens of lambda, sus O(8), sus P(3), and T(11), were found to synthesize none of the DNA structural intermediates. A lysogen believed to be defective in all known phage activities, lambdasus N(7), was found to be able to synthesize an early phage DNA intermediate. The lysogen lambdasus Q(21), defective in late phage functions, is able to synthesize the early phage DNA intermediate and a concatenated molecule of greater molecular weight than the mature lambda DNA.

Early functional mutants of . . . coliphage lambda

The early functional mutants of lambda, belonging to cistrons N, O, and P, are known to be blocked prior to vegetative multiplication of the lambda genome. Superinfection of heteroimmune defective lysogens by these mutants failed to elicit the function required for replication of the superinfecting phage. The mutants among themselves also showed poor cooperation on a nonpermissive host. Studies on the effects of different multiplicities of infection for bacterial lysis showed identical responses for mutants of different cistrons.

Regulation of synthesis of alkaline phosphatase by deoxyribonucleic acid synthesis in a constitutive mutant of Bacillus subtilis

Hiraga, Sota (Osaka University, Osaka, Japan). Regulation of synthesis of alkaline phosphatase by deoxyribonucleic acid synthesis in a constitutive mutant of Bacillus subtilis. J. Bacteriol. 91:2192-2199. 1966.-It was found that synthesis of alkaline phosphatase (APase) correlated with deoxyribonucleic acid (DNA) synthesis in a partially constitutive mutant of Bacillus subtilis. When cultures of the mutant were made to undergo synchronous growth by germination of spores in an excess-phosphate medium, synthesis of APase was repressed at the beginning of DNA synthesis. If the initiation of DNA synthesis was inhibited by thymine starvation, the repression of APase was not observed. When DNA synthesis, previously initiated, was inhibited by thymine or uracil starvation, or by addition of mitomycin C, the repression was partially released at a later stage. In contrast, this correlation between repression and DNA synthesis was not observed in a repressible strain.

Repression of λ-Associated Enzyme Synthesis After λ vir Superinfection of Lysogenic Hosts

Lisio, Arnold L. (National Institutes of Health, Bethesda, Md.), and Arthur Weissbach . Repression of λ-associated enzyme synthesis after λ vir superinfection of lysogenic hosts. J. Bacteriol. 90: 661–666. 1965.—Phage λ vir is a multiple mutant of λ which is capable of overcoming the immunity of a host lysogenic for λ, and initiating normal vegetative replication of the superinfecting phage genome. Superinfection of Escherichia coli K-112 (λ 22 ) with λ vir results in a normal phage yield, lysis time, and H 3 -thymine incorporation compared with infection of the sensitive host, K-112 (S). However, the production of the λ phage-specific early protein, λ-exonuclease, after superinfection of E. coli K-112 (λ 22 ) with λ vir is only 25 to 50% of that obtained from corresponding infection of a nonlysogenic host, E. coli K-112 (S). This repression of λ-exonuclease synthesis is dependent on the C 1 cistron of the prophage and is overcome if the lysogenic host cells are induced prior to superinfection. The data are interpreted as evidence for partial repression of λ vir by the host immunity.