Partial purification and characterization of four endodeoxyribonuclease activities from Escherichia coli K-12

AUTOR(ES)

Blackmore, Robert V.

RESUMO

Four hitherto undescribed endodeoxyribonucleases, temporarily designated A1, A2, A3, and B, have been isolated from E. coli K-12. Each requires Mg++ and is not stimulated by ATP or S-adenosylmethionine. A3 is strongly inhibited by Fe+++ and weakly inhibited by ATP, S-adenosylmethionine, and DPN, whereas B is inhibited by caffeine. Each can be purified free of exonuclease or DNA-3′-phosphatase. A1 (molecular weight approximately 72,000) cleaves single-stranded, circular fd DNA to form 3′-hydroxyl termini and introduces nicks and breaks in the closed, double-stranded replicative form DNA of fd (fd RFI). A2 (molecular weight approximately 46,000) cleaves fd DNA and introduces nicks and breaks in RFI, forming 3′-hydroxyl- and 5′-phosphoryl termini. A3 (molecular weight approximately 38,000) cleaves fd DNA to form 3′-hydroxyl termini and introduces only nicks in fd RFI. Irradiation of the RFI with ultraviolet light markedly increases the rate of hydrolysis by A3. B appears to form 3′-phosphoryl termini with fd DNA, but its characterization is highly preliminary due to its instability.

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