Pneumococcal bacteriophage Cp-1 contains a protein bound to the 5' termini of its DNA

The genome of the pneumococcal bacteriophage Cp-1 has been isolated as a DNA-protein complex. The transfecting activity of this complex is destroyed by treatment with proteolytic enzymes. The DNA-protein complexes do not enter into agarose or acrylamide gels and are retained on glass fiber filters. The protein is specifically associated with the two 5' termini of Cp-1 DNA on the basis of experiments carried out with restriction endonucleases, exonucleases, and radioactive labeling with [gamma-32P]ATP and polynucleotide kinase. The protein component, iodinated in vitro with 125I, has a molecular weight of 28,000 determined by SDS-polyacrylamide gel electrophoresis. The protein remains associated with the Cp-1 DNA after thermal or alkali denaturation, incubation with 6 M guanidinium chloride or 8 M urea, and boiling in 2% SDS, 2% mercaptoethanol, and 6 M urea. When the complex was incubated in 1 M sodium hydroxide or 2.5 M piperidine only a partial breakage of the DNA-protein bond was observed. These results indicate that the 28,000-Da protein is covalently bound to the 5' termini of the DNA.