The DNA-binding domain of nuclear factor I is sufficient to cooperate with the adenovirus type 2 DNA-binding protein in viral DNA replication.

Recombinant baculoviruses have been constructed which express the full-length nuclear factor I (NFI) protein or a derivative of NFI that contains only the DNA-binding domain of the protein in infected insect cells. Both proteins were purified from insect cells infected with the respective baculoviruses and tested for their ability to cooperate with the adenovirus type 2 (Ad2) DNA-binding protein during virus replication. DNase I protection experiments demonstrated that the viral DNA-binding protein increased the affinity of both the full-length NFI and the DNA-binding domain of NFI for their recognition site in the Ad2 origin of DNA replication. As a consequence, the NFI-dependent increase in the efficiency of DNA replication observed upon addition of viral DNA-binding protein was the same when the full-length or DNA-binding domain derivative of NFI was added. Thus it appears that all of the activities associated with the ability of NFI to stimulate Ad2 DNA replication are located within the DNA-binding domain of the protein.