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At least 577 records · Page 32Linked to original sources
PubMed1967

Behavior of lambda bacteriophage in a recombination deficienct strain of Escherichia coli.

The behavior of lambda phage in the Rec(-) strain JC-1569 is compared with that in the Rec(+) strain JC-1557. No difference deemed significant was noted in the adsorption rate, latent period, burst size, frequency of lysogenization, and frequency of vegetative phage recombination. The location of the prophage and its mode of insertion in the Rec(-) lysogen of wild-type lambda (lambda(+)) were inferred to be normal from the results of conjugational crosses. Spontaneous and ultraviolet (UV) irradiation induction of lambda(+) were markedly reduced in the Rec(-) lysogen. On the other hand, thermal induction of a mutant lambda (lambdacI857) lysogen of the Rec(-) strain was not reduced and was only slightly affected by UV irradiation. Phage subject to inhibition by lambda immunity failed to multiply in UV-irradiated cells of the Rec(-) lambda(+) lysogen, whereas those not inhibited by this immunity did multiply. It was concluded that the failure of UV to induce lambda(+) in the Rec(-) lysogen was not due to damage to the prophage, but rather to the inability of the irradiated cells to respond by lifting immunity. Preliminary evidence indicates that a single mutation confers recombination deficiency and the inability to lift immunity after UV irradiation. Possible relationships between recombination and the lifting of immunity are enumerated.

Coliphages↗
PubMed1967

Differential expression of bacteriophage genomes in vegetative and sporulating cells of Bacillus subtilis.

Two antigenically distinct bacteriophages, beta3 and beta22, have been isolated and characterized with Bacillus subtilis strain W23 as a host. They differ in plaque morphology, single-step growth characteristics, host range, and thermal stability. The deoxyribonucleic acids isolated from beta3 and beta22 differ in base composition, density in CsCl and Cs(2)SO(4), sedimentation coefficient, molecular weight, and thermal denaturation temperature. These phages have been used to analyze the ability of B. subtilis to sporulate despite infection by virulent phages. When development of phages beta3 and beta22 in sporulating cultures was compared with that in log cultures, an increase in the latent periods of infection and a decrease in the burst sizes for the two phages were observed. Sporulating cultures infected with beta3 yielded the usual percentage (85%) of mature spores; 80% of these contained phage determinants and 20% were uninfected. However, cultures infected with beta22 lysed. Of the small fraction (0.01%) which sporulated, 83% were uninfected and 17% were infected. Phage beta3-infected and uninfected spores were examined to distinguish any chemical or physical differences. Preparations of both types of spore contained 81.4 mug of dipicolinic acid per mg (dry weight), and examination by phase-contrast microscopy gave no evidence of any difference in outward appearance. A 20% decrease in infected spore count was observed upon heating at 80 C for 10 min. Differences in the infection processes of the two phages prompted an analysis of the transcription process after infection. Deoxyribonucleic acid-ribonucleic acid hybrid analysis of relative amounts of phage-specific and host-specific messenger ribonucleic acid (mRNA) present in infected cells suggested that beta3 was unable to repress the synthesis of host mRNA and that beta3-specific mRNA synthesis was repressed in sporulation-phase cultures. Phage beta22, in contrast, was able to repress host-specific mRNA synthesis in both log-infected and sporulation-infected cells. The results suggest that the differential expression of the phage genomes is due to the relative ability of the phages to repress the host genome.

Bacillus subtilis↗
PubMed1968

Genetic relatedness studies with adenovirus-associated viruses.

Adenovirus-associated viruses (AAV) contain double-stranded deoxyribonucleic acid (DNA). DNA from each of the four AAV serotypes was used as template for the in vitro synthesis of complementary (3)H-ribonucleic acids(RNA). An estimation of genetic interrelatedness was made on the basis of hybridization reactions between synthetic AAV RNA and AAV DNA. Heterologous reactions were 27 to 37% of homologous reactions, suggesting that the AAV serotypes are related to about the same extent. AAV-1 synthetic RNA was also reacted with DNA from helper adenovirus types 2, 7, and SV15. Very low levels of RNA binding were observed, but it is not likely that these reactions represent AAV-adenovirus genetic relatedness.

Adenoviridae↗
PubMed1969

Control of gene function in bacteriophage T4. I. Ribonucleic acid and deoxyribonucleic acid metabolism in T4rII-infected lambda-lysogenic hosts.

Deoxyribonucleic acid (DNA) synthesis in T4rII-infected, lambda-lysogenic strains of Escherichia coli proceeds with one-half the rate of T4 wild-infected bacteria and stops 16 min after infection at 37 C. The rates of ribonucleic acid (RNA) synthesis, however, are the same with T4rII and T4 wild. The turnover of pulse-labeled RNA is slow in K strains (half-lives 10 to 20 min) as compared with B strains (half-lives 2.5 to 6 min). Lambda-lysogeny increases the apparent messenger (m) RNA half-lives in pulse-chase experiments. The shutoff of host RNA synthesis in T4rII infected K(lambda) is incomplete. Moreover, the preferential transcription of T4 DNA ceases 13 min after infection, and transcription of host and prophage lambda DNA is resumed. The T4 RNA synthesized in rII-infected K(lambda) contains no late T4 mRNA. The early portion of the T4 genome, however, is transcribed completely. The T4-induced early modification of bacterial RNA polymerase does occur. Resumption of host DNA transcription at 13 min after infection is not associated with a reversal of the above polymerase modification. It is concluded that in lambdalysogenic bacteria T4rII infections are abortive because RNA polymerase is prevented from transcribing late T4 genes.

Centrifugation, Density Gradient↗
PubMed1970

Studies on the in vitro assembly of bacteriophage phi 80 and phi 80-lambda hybrids.

Suppressor-sensitive (sus) mutants of bacteriophage phi80 defective in late functions were classified, by means of in vitro assembly tests, into two complementation groups: head donors and tail donors. Each group of mutants was subdivided, by means of two-factor crosses, into six cistrons. Deletion mapping revealed clustering of tail and also of head cistrons. The two clusters were located in the left arm of vegetative phi80 (the tail specifying cluster being distal). In vitro cross complementation between phi80 and lambda sus mutants revealed that whereas lambda heads could quite efficiently bind phi80 tails to form viable phage, the union of phi80 heads and lambda tails was very much less efficient. Deletion mapping of the phi80 sus mutants, using both phi80 and i(phi80)h(lambda) deletion lysogens indicated congruent gross gene arrangement in the two related bacteriophages.

Coliphages↗
PubMed1970

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.

Arabinose↗
PubMed1970

Quantitative characteristics of the transformation of hamster cells by PARA (defective simian virus 40)-adenovirus 7.

An in vitro method for the quantitative measurement of transformation in hamster embryo fibroblasts by the PARA [defective simian virus 40 (SV40)]-adenovirus 7 hybrid has been developed. Transformation by PARA particles followed one-hit kinetics with a ratio of 1 focus-forming unit per 250 plaque-forming units. The method of viral adsorption had a direct effect upon the total number of foci which developed but not on the quantitative aspects of this assay. A fluorescent-focus assay was developed which provided a direct correlation of the observed morphological transformation and the presence of the PARA genome. This fluorescent-focus assay utilized detection of the SV40 tumor antigen, which was present in all foci transformed by PARA. Single foci induced by PARA were isolated and grown into cell lines. Two types of foci were observed and isolated; the first contained cells having a cuboidal or SV40-type morphology, and the second consisted of epithelial or adenovirus-type transformed cells. Both types contained the SV40 tumor and SV40 surface antigens as determined by the indirect fluorescence technique; however, only the epithelial cells contained the adenovirus 7 tumor antigen. All five cell lines which were injected into weanling Syrian hamsters were found to be oncogenic. These cell lines induced antibodies to both SV40 and adenovirus 7 tumor antigens in tumor-bearing animals.

Adenoviridae↗
PubMed1970

Inhibition of host protein synthesis during infection of Escherichia coli by bacteriophage T4. II. Induction of host messenger ribonucleic acid and its exclusion from polysomes.

Two gene clusters on the Escherichia coli chromosome were induced at early times after T4 infection when >99% of the cells were infected: the lactose (lac) operon and prophage lambda. Their messenger ribonucleic acid (mRNA) was detected by hybridization to phi80 dlac deoxyribonucleic acid (DNA) and lambdaDNA, respectively. Synthesis of host mRNA could be initiated during the first few minutes after T4 infection, although no beta-galactosidase activity could be detected. Hybridization analyses of selected fractions from sucrose gradients revealed that most of this lac mRNA induced at very early times of T4 infection was not associated with ribosomes. In contrast, virtually all lac mRNA in uninfected bacteria was associated with polysomes. This exclusion affected all host mRNA; about 70% of E. coli(3)H-mRNA, labeled from 2 to 3 min after T4 infection, was excluded from polysomes. Infection even reduced the yield of beta-galactosidase from lac mRNA induced before infection. Gradients from rifampicin-inhibited cells showed the normal growth of lac mRNA polysomes; in contrast, T4 infection prevented growth of the preinduced lac polysomes. It is concluded that T4 infection interferes within seconds with the reassociation of ribosomes to host mRNA.

Animals↗
PubMed1970

Lambda mutants which persist as plasmids.

Lambda phages mutated in gene N do not kill sensitive host bacteria, but persist as plasmids. Plasmids are formed by genomes containing cI(+), and also by sus, ts, or c mutants of cI. Bacteria infected with two or more phage particles give rise to clones in which most of the bacteria are carriers. The introduced lambda genomes replicate more than once per bacterial division until there are 10 to 20 lambda plasmids per host genome. In bacteria containing both F and lambda plasmids, both replicate independently, and elimination by growth in acridine orange is also independent. Carriers of lambda Nsus plasmids are not immune, and there is complementation between the plasmids and superinfecting lambda mutants.

Acridines↗
PubMed1970

Integration of the deoxyribonucleic acid of adenovirus type 12 into the deoxyribonucleic acid of baby hamster kidney cells.

In a previous report, evidence was presented that the deoxyribonucleic acid (DNA) of adenovirus type 12 (Ad12) is integrated by covalent linkage into the DNA of baby hamster kidney cells (BHK-21 cells). These studies have been extended. The DNA of Ad12 and that of BHK-21 cells grown in medium containing 5-bromodeoxyuridine could be separated by equilibrium centrifugation in alkaline CsCl density gradients. BHK-21 cells were infected with (3)H-labeled Ad12, and the total intracellular DNA was analyzed at various times after infection in alkaline CsCl density gradients. The (3)H label in the position of cellular DNA hybridized predominantly with viral DNA and to a lesser extent also with cellular DNA. Replication of viral DNA could not be detected in BHK-21 cells. The appearance of viral (3)H label in the density stratum of cellular DNA was not significantly affected when DNA synthesis in Ad12-infected BHK-21 cells was inhibited >96% by cytosine arabinoside. These findings provided additional evidence for integration of Ad12 DNA into the DNA of BHK-21 cells. It could be calculated that 5 to 55 Ad12 DNA equivalents per cell are integrated. Replication of viral or cellular DNA was not required for integration. Inhibition of protein or ribonucleic acid synthesis interfered with integration only slightly.

Adenoviridae↗
PubMed1970

Synthesis of messenger ribonucleic acid after bacteriophage T1 infection.

Synthesis of host-specific and phage-specific messenger ribonucleic acid (mRNA) was studied in bacteria infected by unmodified (T1 . B) or modified [T1 . B(P1)] bacteriophage T1. In a "standard" infection of Escherichia coli B by T1 . B (no host-controlled modification involved), the rate and amount of T1 mRNA synthesis was intermediate between those values reported for infections by a virulent phage such as T4 or a temperate phage such as lambda. The initial rate of mRNA synthesis was slightly increased after T1 . B(P1) infection of E. coli B in comparison with T1 . B infection of the same host. Little or no phage mRNA synthesis could be detected in T1 . B infection of E. coli B(P1). Phage mRNA synthesis in T1 . B(P1)-infected E. coli B(P1) cells was approximately the same in amount as that seen in T1 . B(P1) infection of E. coli B. Synthesis of host-specific mRNA continued throughout the latent period in all infections studied. However, the enzyme beta-galactosidase could not be induced, except after T1 . B infection of E. coli B(P1). In an attempt to understand the apparent differences in mRNA synthesis after infection of E. coli B by phages T1 . B or T1 . B(P1), the effect of altered T1 deoxyribonucleic acid (DNA) methylation on mRNA synthesis was studied. Methyl-deficient T1 DNA, made in cells infected with ultraviolet-irradiated phage T3, inhibited (14)C-uridine incorporation more strongly than normal T1. One passage of methyl-deficient T1 through E. coli B restored uracil incorporation rates to those seen with ordinary T1. This suggests that methylation of T1 DNA can influence the rate of phage mRNA synthesis. However, attempts to relate the difference in mRNA synthesis seen between T1 . B and T1 . B(P1) in E. coli B to the activity of the P1 modification gene were not conclusive.

Carbon Isotopes↗