Identification of a protein linked to the ends of adenovirus DNA.

A DNA-protein complex from human adenoviruses has been further characterized by electron microscopy, radiochemical labeling and analytical ultracentrifugation. Preparations of the complex contain a large percentage of forms of DNA which are either circular or oligomeric and are readily distinguishable from preparations of pronase-treated adenovirus DNA by analytical ultracentrifugation in cesium chloride gradients containing 4 M guanidinium chloride. The protein component has been iodinated in vitro with ¹²⁵I using Bolton and Hunter reagent, and SDS-polyacrylamide gel analysis of the labeled protein indicates that it has an apparent molecular weight of 55,000 daltons. DNAase I digestion of the DNA-protein complex labeled with ³²PO₄ results in release of a ³²PO₄-labeled protein which remains labeled even after boiling in 1% SDS and 1% mercaptoethanol. Subsequent digestion of this entity with snake venom phosphodiesterase leads to release of ³²P₄-labeled 5′-phosphate deoxynucleotides. Digestion of the DNA-protein complex with Eco R1 and analysis of the isolated restriction fragments indicates that the protein is present on each terminal fragment. We conclude that there is a protein of 55,000 daltons directly attached to each 5′ end of molecule probably via a covalent linkage. We propose that the protein functions during DNA replication by facilitating priming of the progeny strands, thus allowing the 5′ ends of the DNA to be replicated.