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Biomedical subjects

M Sekiguchi

Publications and source records attributed to M Sekiguchi.

At least 577 records · Page 32Linked to original sources
PubMed1983

A new gene (alkB) of Escherichia coli that controls sensitivity to methyl methane sulfonate.

Seven mutants of Escherichia coli were isolated that are sensitive to methyl methane sulfonate but not to UV light. They exhibited decreased host cell reactivation capacity for methyl methane sulfonate-treated phage lambda. Five of the mutations were mapped in the same region as alkA (previously called alk) and may indeed be identical to known mutations. Another mutation was found near nalA, and the gene responsible was named alkB. Its phenotype was different from that of ada, since the alkB mutant exhibited a normal adaptive response to N-methyl-N'-nitro-N-nitrosoguanidine. A third type of mutation was mapped near polA, but this mutant contained an almost normal level of DNA polymerase I activity.

Drug Resistance, Microbial↗
PubMed1983

Isolation of conditional lethal mutator mutants of Escherichia coli by localized mutagenesis.

By using localized mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine, we isolated 39 temperature-sensitive growth mutants that exhibited high mutability when the bacteria were grown at the permissive temperature. Two of the mutations, dnaQ186 and dnaQ231, were shown to be new alleles of the dnaQ gene by genetic mapping and complementation tests with the dnaQ49 mutation previously isolated. They shared common properties with the dnaQ49 strain, but their mutator activity was not temperature dependent. The dnaQ mutants exhibited increased sensitivity to inhibitors of DNA gyrase and to DNA intercalating and alkylating agents.

Alleles↗
PubMed1983

Ventriculographic findings in the convalescent stage in eleven cases with acute myocarditis.

In order to clarify the sequelae of 11 patients who suffered from acute myocarditis of viral origin and were diagnosed by endomyocardial biopsy in the early and the convalescent stage of the disease, left ventriculograms were obtained from 17 to 167 (46.5 +/- 41.2, mean +/- SD) days after the onset of the disease were analyzed. The data were compared with the biopsy findings in the convalescent stage. The mean left ventricular ejection fraction (LVEF) was 57.5 +/- 10.8% and in 3 cases the LVEF was less than 50%. In 2 cases, apparent asyneresis was observed. In all cases coronary arteriographic findings did not show significant stenosis. It is concluded that after viral myocarditis, increase in left ventricular end-diastolic volume, depressed ejection fraction and asyneresis occur in some cases and it can be said that a development from myocarditis to dilated cardiomyopathy occurs.

Acute Disease↗
PubMed1983

[Unstable angina].

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Angina Pectoris↗
PubMed1983

[Tumor suppressing effect of systemic hyperthermia with 2350 MHz microwaves combined with 5-fluorouracil in mice].

C3H/He mice were inoculated i.p. with syngeneic MM2 tumor cells (2 X 10(6) cells/mouse), and they were subsequently treated by systemic hyperthermia with microwave irradiation (2450 MHz) alone, administration of 5-FU alone, or a combination of the both. The mice were exposed to hyperthermia for 5 minutes everyday with an output of 10, 20 or 30 watts. 5-FU was administered i.p. for 3 days at dose levels of 2.5 mg/kg, 5 mg/kg or 10 mg/kg body weight. The mean survival time and the mean relative body weight were recorded. From these data, tumor-suppressing effects of the treatments were analyzed by one-way variance analysis or two-way variance analysis. The mice treated with microwave irradiation alone or 5-FU alone survived significantly longer than the control mice receiving no treatment (P less than 0.01). However, no significant difference in mean survival time was observed between the microwave group and the 5-FU group. The mean relative body weight was similar among the microwave, the 5-FU and the control group. When the mice were treated with microwave irradiation and 5-FU, significant difference was observed in the mean survival time (P less than 0.01), and the combination of microwave irradiation with an output of 20 W and 10 mg/kg of 5-FU seemed to be optimal. Determination of an optimal combination was difficult with the mean relative body weight, because body weight decreased due to side effect of the combination therapy.

Animals↗
PubMed1983

[Experimental study on the anti-tumor effect of microwaves].

C3H/He mice bearing a mammary carcinoma, MM2, were treated by systemic hyperthermia with microwave irradiation (2450 MHz). An output of 30 watts of microwaves for 5 min at a distance of 20 cm from the animal raised and maintained the rectal temperature of mice to higher than 42 degrees C for 2.2 min and higher than 40 degrees C for 10.2 min. The mice were inoculated i. p. with MM2 tumor cells (2 X 10(6) cells/mouse), and then they were exposed to hyperthermia every day; 10 watts for 2, 4, or 6 min, or 20 watts for 2, 4, 6 min. The control mice receiving no irradiation and the mice treated with irradiation of 10 watts for 2 min or 20 watts for 2 min died within 21-23 days. Whereas, 40 percent of the mice treated with microwave irradiation of 10 watts for 4 or 6 min, or 20 watts for 4 or 6 min survived longer than 30 days. The 6 mice, which survived longer than 120 days, were challenged by reinoculation with MM2 tumor cells (2 X 10(6)cells/mouse). All the mice but one survived longer than 30 days with no accumulation of ascites. These experimental data suggest that the systemic hyperthermia with microwave irradiation (24 50 MHz) might suppress the tumor growth in vivo.

Animals↗
PubMed1982

Purification and characterization of normal and mutant forms of T4 endonuclease V.

Endonuclease V of bacteriophage T4 has been purified to physical homogeneity from T4D-infected Escherichia coli 1100. The enzyme, whose molecular weight is 16,000, possessed two distinct catalytic activities, a pyrimidine dimer-DNA glycosylase and an apurinic/apyrimidinic endonuclease. They acted on UV-irradiated poly(dA) . poly(dT) in a sequential manner; the glycosylase cleaved the N-glycosyl bond between the 5'-pyrimidine of a dimer and the corresponding sugar and then the endonuclease hydrolyzed a phosphodiester bond on the 3'-side of the apyrimidinic site. The 5'-termini thus generated were phosphorylated by T4 polynucleotide kinase only after they had been subjected to direct photoreversal and then treated with alkaline phosphatase. By using two phage mutants, uvs-5 and uvs-13, it was shown that occurrence of an amber mutation in the denV gene caused a simultaneous loss of the two activities. Suppression of the mutation of uvs-5 rendered both activities partially active. When the mutation of uvs-13 was suppressed, a mutant form of enzyme that possessed only a glycosylase activity was produced. This suggests that there are two distinct domains in a single enzyme, each of which corresponds to one of the activities.

Deoxyribonuclease (Pyrimidine Dimer)↗
PubMed1982

Large-scale selection and analysis of temperature-sensitive mutants for cell reproduction from BHK cells.

Temperature-sensitive (ts) mutant cells for cell reproduction were isolated from the Syrian hamster cell line BHK21/13 by multiple culturing in the presence of 5-fluoro-2'-deoxyuridine (FdU) at 37.5 degrees after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis. A simple method for cell fusion was devised, which enabled us to perform complementation studies with a large number of ts mutants. By using the method we have analyzed 219 ts mutants and classified them into 18 complementation groups. Mutants that belonged to the same complementation groups tended to exhibit similar patterns of inhibition of DNA synthesis at 39.5 degrees; however, some mutants belonging to the same group showed somewhat different patterns, probably due to occurrence of different mutations in the same gene. Distribution of the ts mutants among the 18 complementation groups was uneven; more than 50% of the mutants examined were assigned to complementation group B and G. The mutations belonging to complementation group B and G were found to be linked to the X chromosome.

Animals↗
PubMed1982

Action of T4 endonuclease V on polydeoxyribonucleotides with apyrimidinic or apurinic sites.

[3H]Thymine-labeled poly(dA) . poly(dT) carrying many apyrimidinic (AP) sites has been prepared by treating an enzymatically synthesized poly(dA) . poly(dT, dU) with uracil-DNA glycosylase. Incubation of the polymer with a homogeneous preparation of T4 endonuclease V resulted in conversion of the labeled material into acid-soluble forms. Native DNA with apurinic sites was also cleaved by the enzyme. Single-stranded polymers, poly(dT) carrying AP sites or poly(dT) with thymine dimers, were barely attacked by T4 endonuclease V. The polymer whose aldehyde moieties at AP sites were reduced to alcoholic forms was not susceptible to the enzyme. The site of endonucleolytic cleavage was determined by using alternating copolymers whose phosphate groups were differentially labeled. The result is consistent with the view that T4 endonuclease V cleaves a phosphodiester linkage on the 3'-side of AP sites, producing chains terminated at their 3'-ends with base-free deoxyribose and at their 5'-ends with phosphate.

Binding Sites↗