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Biomedical subjects

M Sekiguchi

Publications and source records attributed to M Sekiguchi.

At least 685 records · Page 38Linked to original sources
PubMed1976

Further purification and characterization of T4 endonuclease V.

T4 endonuclease V, which is involved in repair of ultraviolet-damaged DNA, has been purified 3600 fold from T4D-infected Escherichia coli. The enzyme shows optimal activity at pH 7.2 and does not require added divalent ions. Endonuclease V attacks both native and heat-denatured DNA provided that the DNA has been irradiated, and the enzyme activity is dependent on the dose of ultraviolet irradiation. The rate and the extent of the reaction are greater with irradiated native DNA although the Km values for the two types of DNA are the same (2.25 - 10(-5) M). The enzyme is readily inactivated by heat and is sensitive to p-chloromercuribenzoate. Endonuclease V-treated irradiated DNA is degraded by spleen phosphodiesterase only when the DNA has been treated with alkaline phosphatase, suggesting that the enzyme produces 5'-phosphoryl termini.

Alkaline Phosphatase↗
PubMed1976

Repair of DNA damaged by methyl methanesulfonate in bacteriophage T4.

A highly purified preparation of T4 endonuclease V does not degrade DNA alkylated with methyl methanesulfonate, and the methyl methanesulfonate sensitivity of T4 wild type and x mutant is not affected by the v mutation. Thus, T4 endonuclease V, the v gene product, does not seem to be involved in a repair or an abortive repair of methyl methanesulfonate-damaged T4 DNA. The x and y genes of T4 and the polA and the uvrD genes of Escherichia coli are concerned with the repair of methyl methanesulfonate-induced damages in T4 DNA. Since effects of the polA and the x or y mutations are additive, it is supposed that there are at least two pathways for the repair of methyl meth-anesulfonate-damaged T4 DNA, one controlled by the x and the y genes and the other in which E. coli DNA olymerase I is involved. The partial suppression of the x gene mutation at high temerature was also demonstrated.

Coliphages↗
PubMed1976

5' leads to 3'-Exonucleases of bacteriophage T4.

Two enzyme activities which release nucleotides preferentially from the 5' termini of DNA were found in T4-infected Escherichia coli. Since no corresponding activities were found in uninfected cells, the activities appeared to be induced by T4. Both activities are capable of excising pyrimidine dimers from ultraviolet-irradiated DNA which has been treated with T4 endonuclease V. One of the activities , referred to as T4 exonuclease B, was purified 400-fold from an extract of T4v 1- infected cells. The enzyme initiates hydrolysis of DNA specifically at the 5' termini to yield products which are mainly oligonucleotides of varying length. The hydrolysis reaction proceeds in a limited manner. The enzyme shows optimal activity at pH 7.0 and absolutely requires Mg2+. The molecular weight of the enzyme , as estimated by gel filtration, is approximately 35,000. Another activity, referred to as T4 exonuclease C, was purified 240-fold from the extract. This activity also excises pyrimidine dimers from ultraviolet-irradiated, incised DNA and releases nucleotides at 5' termini. It has a pH optimum at 7.5 and requires Mg2+. The molecular weight of the enzyme is approximately 20,000.

Coliphages↗
PubMed1976

A 4-year survival rate after cardiac pacing in A-V block in the heart institute of Japan.

The long-term prognosis after cardiac pacing in A-V block was assessed by a follow-up study of 59 patients in whom pacing had been introduced 4 years or more before analysis. The 1 year survival rate was 85% and the 4 year survival rate was 71%. These figures are substantially better than the survival rate reported in patients not paced. The mortality has been higher in patients older than 70 years old. Even though patients were reviewed monthly or every 3 months in a pacemaker clinic, there were 3 sudden deaths in 4 years.

Adams-Stokes Syndrome↗
PubMed1975

Action of exonuclease V (the recBC enzyme) on ultraviolet-irradiated DNA.

Exonuclease V (the recBC enzyme) of Escherichia coli can release pyrimidine dimers from ultraviolet-irradiated linear duplex DNA though it acts more slowly on irradiated DNA than on non-irradiated DAN. However, close circular lambda-dv DNA or phi X174 replicative form I DNA is not attacked by exonuclease V even though the DNA has been irradiated and treated with T4 endonuclease V to produce single-stranded breaks at the 5'-side of pyrimidine dimers. When irradiated circular DNA, previously nicked by T4 endonuclease V, is briefly exposed to elevated temperature, the DAN becomes susceptible to the action of exonuclease V, and pyrimidine dimers are selectively released. The increased susceptibility to exonuclease V may be resulted from locarized denaturation, or "fraying" of the 5'-termini at the nicks. The preferential release of pyrimidine dimers was observed when irradiated DNA, treated with T4 endonuclease V, was incubated with crude extracts of Escherichia coli. The activity was found in various strains defective in exonuclease V and/or DNA polymerase I.

Coliphages↗