Template activating factor I, a novel host factor required to stimulate the adenovirus core DNA replication

The adenovirus (Ad) genome in virion exists in the form of the Ad core, which is a complex of Ad DNA and viral basic proteins. The Ad core supported only initiation and limited elongation in DNA replication in a cell-free system which was developed for DNA replication of naked Ad DNA. We found that addition of a cytoplasmic fraction from uninfected HeLa cells on the top of the system stimulated Ad core DNA replication, although it had no effect on DNA replication of naked Ad DNA. The factor stimulating Ad core DNA replication, designated as template activating factor I (TAF-I), was purified by successive steps of ammonium sulfate precipitation, column chromatographies on phosphocellulose and Q-Sepharose, and glycerol density gradient centrifugation. SDS-polyacrylamide gel electrophoresis of the purified fraction revealed the presence of proteins with molecular masses of 41 and 39 kDa. TAF-I stimulated both initiation and elongation in Ad core DNA replication. Judging from its behavior in purification steps, TAF-I could be acidic. These findings suggest that TAF-I stimulates Ad core DNA replication by interaction with viral basic core proteins.