Filamentous cells resulting from growth of a dnaEts mutant of Escherichia coli at high temperature were stimulated to divide by infection with bacteriophage T4. The effect appears to be related to T4 DNA synthesis; no increase in cell number took place in chloramphenicol-treated. T4-infected cells nor in cells infected with DNA synthesis-less mutants of T4. The ability of cells to divide after T4 infection was dependent on the length of time that the cells had been grown at 42 degrees C, indicating that a potential for cell division accumulates during preincubation.

Cell Division↗

PubMed1977

Replication of plasmid pSC101 in Escherichia coli K12: requirement for dnaA function.

Replication of pSC101 was analyzed by using DNA-DNA hybridization and alkaline sucrose gradient centrifugation. Mutants of the dnaA gene were tested for their capacity to replicate pSC101 DNA at a non-permissive temperature. Only a small amount of radioactive precursor was incorporated into pSC101 DNA in dnaA mutants at 42 degrees C whereas active incorporation into plasmid DNA took place in dnaA+ strain under the same conditions. The effect of the dnaA mutation was grater on plasmid DNA synthesis than on host chromosomal DNA synthesis. The numbers of copies of pSC101 per chromosome in wild type and dnaA strains, grown at 30 degrees C, were about 8 and 2, respectively. These results indicate that the dna A gene product is required for the replication of pSC101 DNA.

Chromosomes, Bacterial↗

PubMed1977

Effects of the combination of tumor-specific and nonspecific immunization on tumor suppression.

The crushed whole Aoyama B cells attached to oil droplets were found to be most suitable for the adjuvant effect of Mycobacterium tuberculosis against tumor growth when judged by the criterion of effectiveness and a clinical application with minimal side effects. The immunogenicity of tumor cells was well stabilized and maintained with a suitable concentration of formalin; this was less than 1% and the optimum concentration was 0.05% or 0.1%. When the tumor cells treated with the optimum concentration of formalin were combined with suitable adjuvant, immunoprotection against the tumor progress was accelerated.

Adjuvants, Immunologic↗

PubMed1977

[Molecular biological aspects of the problems of human genetics (author's transl)].

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DNA Repair↗

PubMed1977

Specific action of T4 endonuclease V on damaged DNA in xeroderma pigmentosum cells in vivo.

The specific action of T4 endonuclease V on damaged DNA in xeroderma pigmentosum cells was examined using an in vivo assay system with hemagglutinating virus of Japan (Sendai virus) inactivated by UV light. A clear dose response was observed between the level of UV-induce unscheduled DNA synthesis of xeroderma pigmentosum cells and the amount of T4 endonuclease V activity added. The T4 enzyme was unstable in human cells, and its half-life was 3 hr. Fractions derived from an extract of Escherichia coli infected with T4V1, a mutant defective in the endonuclease V gene, showed no ability to restore the UV-induced unscheduled DNA synthesis of xeroderma pigmentosum cells. However, fractions derived from an extract of T4D-infected E. coli with endonuclease V activity were effective. The T4 enzyme was effective in xeroderma pigmentosum cells on DNA damaged by UV light but not in cells damaged by 4-nitroquinoline 1-oxide. The results of these experiments show that the T4 enzyme has a specific action on human cell DNA in vivo. Treatment with the T4 enzyme increased the survival of group A xeroderma pigmentosum cells after UV irradiation.

4-Nitroquinoline-1-oxide↗

PubMed1977

Action of T4 endonuclease V on DNA containing various photoproducts.

The action of T4 endonuclease V on DNA containing various photoproducts was investigated. (1) The enzyme introduced strand breaks in DNA from ultraviolet-irradiated vegetative cells of Bacillus subtilis but not in DNA from irradiated spores of the same organism. DNA irradiated with long wavelength (360 nm peak) ultraviolet light in the presence of 4,5',8-trimethylpsoralen was not attacked by the enzyme. These results indicate that 5-thyminyl 5,6-dihydrothymine (spore photoproduct) and psoralen mediated cross-links in DNA are not recognized by T4 endonuclease V. (2) DNA of phage PBS1, containing uracil in place of thymine, and DNA of phage SPO1, containing hydroxymethyluracil in place of thymine, were fragmented by the enzyme when the DNA's had been irradiated with ultraviolet light. T4 endonuclease V seems to act on DNA with pyrimidine dimers whether the dimers contain thymine residues or not.

DNA↗

PubMed1977

Mutations of temperature sensitivity in R plasmid pSC101.

Temperature-sensitive (Ts) mutant plasmids isolated from tetracycline resistance R plasmid pSC101 were investigated for their segregation kinetics and deoxyribonucleic acid (DNA) replication. The results fit well with the hypothesis that multiple copies of a plasmid are distributed to daughter cells in a random fashion and are thus diluted out when a new round of plasmid DNA replication is blocked. When cells harboring type I mutant plasmids were grown at 43 degrees C in the absence of tetracycline, antibiotic-sensitive cells were segregated after a certain lag time. This lag most likely corresponds to a dilution of plasmids existing prior to the temperature shift. The synthesis of plasmid DNA in cells harboring type I mutant plasmids was almost completely blocked at 43 degrees C. It seems that these plasmids have mutations in the gene(s) necessary for plasmid DNA replication. Cells haboring a type II mutant plasmid exhibited neither segregation due to antibiotic sensitivity nor inhibition of plasmid DNA replication throughout cultivation at high temperature. It is likely that the type II mutant plasmid has a temperature-sensitive mutation in the tetracycline resistance gene. Antibiotic-sensitive cells haboring type III mutant plasmids appeared at high frequency after a certain lag time, and the plasmid DNA synthesis was partially suppressed at the nonpermissive temperature. They exhibited also a pleiotrophic phenotype, such as an increase of drug resistance level at 30 degrees C and a decrease in the number of plasmid genomes in a cell.

DNA, Bacterial↗

PubMed1977