Genome-linked protein associated with the 5' termini of bacteriophage phi29 DNA

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Abstract
A DNA-protein complex was isolated from Bacillus subtilis bacteriophage .vphi.29 by sucrose gradient sedimentation or gel filtration in the presence of agents known to break noncovalent bonds. A 28,000 dalton protein was released from this complex by subsequent hydrolysis of the DNA. The DNA-protein complex was examined for its susceptibility to enzymes which act upon the 5'' and 3'' termini of DNA molecules. It was susceptible to exonucleolytic degradation from the 3'' termini by exonuclease III but not from the 5'' termini by .lambda. [phage] exonuclease. Attempts to label radioactively the 5'' termini by phosphorylation with [phage] T4 polynucleotide kinase were unsuccessful despite prior treatment with alkaline phosphatase or phosphatase treatment of denatured DNA. Removal of the majority of the bound protein by proteolytic digestion did not increase susceptibility. The linked protein is probably covalently attached to the 5'' termini of .vphi.29 DNA.