EFFECTS OF DIVALENT CATIONS ON THE CONVERSION OF BACTERIOPHAGE M13 AND ΦX174 DNAS TO THEIR REPLICATIVE FORMS BY EXTRACTS OF ESCHERICHIA COLI

Abstract

The conversion of single-stranded circular DNA of bacteriophage M13 or φX174 to the double-stranded form by cell-free extracts of Escherichia coli requires Mg²⁺ as a cofactor. In this report, it was examined whether any other divalent cation could substitute for Mg²⁺ as a cofactor at the replication of these DNAs. The results showed that Mn²⁺, Co²⁺, Sr²⁺, and Ba²⁺ could replace Mg²⁺ The replacement, however, induced some abnormal synthesis of DNA. The DNA synthesized with Mn²⁺ or Sr²⁺ contained several interruptions in the synthesized strand. The synthesis of DNA seems to be initiated at several points on the identical template. The DNA synthesized with Mn²⁺, Co²⁺, or Sr²⁺ had plaque-forming ability, and the product synthesized with Mn²⁺, or Co²⁺ but not with Sr²⁺, showed high frequencies of mutation. Although the synthesis of φX174 DNA was not inhibited by rifampicin when Mg²⁺ was used as a cofactor, it was inhibited when Mn²⁺ or Sr²⁺ was used instead of Mg²⁺.