Complex-Formation by protein and nucleic acid: I. Evidence for specific interaction between ΦX174 phage protein and ΦX174 phage deoxyribonucleic acid in vitro

Abstract

1. 1. ΦX174 phage protein is capable of interacting specifically with ФX174 phage DNA in the presence of Ca 2+, and the complex thus formed can be adsorbed to intact cells of Escherichia coli C. Phage DNA, initially sensitive to treatment with deoxyribonuclease, becomes resistant on contact with protein and subsequently with the cells. 2. 2. Preincubation of ΦX174 DNA with deoxyribonuclease results in a marked reduction in complex formation. Native double-stranded DNA, heat-denatured single-stranded or ultrasonically denatured DNA from E. coli have no ability to carry out this specific reaction. A fraction obtained by centrifugation at 105 000 × g for 2 h from E. coli C does not interact with ФX174 DNA. Ca 2+ can be effectively replaced by Zn 2+, Cd 2+ or Mn 2+ but not by Mg 2+, Cu 2+ or Ba 2+. 3. 3. When ФX174 DNA is incubated with ΦX174 protein for 12 h in the presence of Ca 2+, a complex in which DNA is contained in a form resistant to treatment with deoxyribonuclease is produced without additional incubation with the cells. It is therefore concluded that the ΦX174 DNA becomes surrounded by phage protein, producing a complex similar to the intact phage particle, after incubation for a longer time.