Transcriptional repression of K-Rta by Kaposi's sarcoma-associated herpesvirus K-bZIP is not required for oriLyt-dependent DNA replication

Kaposi's sarcoma-associated herpesvirus origin-dependent DNA replication requires the core replication proteins plus K-Rta and K-bZIP. To determine which K-bZIP protein domains contribute to oriLyt-dependent DNA replication and facilitate suppression of K-Rta-mediated transcriptional activation, we generated a series of deletion constructs and site-directed mutations within the K-bZIP ORF. Mutation of key leucine residues within the putative leucine zipper (LZ) motif eliminated the ability of the protein to homodimerize and complement oriLyt-dependent DNA replication. Deletion of the basic amino acid region (BR) or LZ domain did not affect the ability of K-bZIP to bind to K-Rta indicating that either region contributes to heterodimerization with K-Rta. However, deletions or mutations introduced into both the LZ and BR resulted in elimination of the suppressive activity of K-bZIP even in the presence of a K-bZIP–K-Rta interaction. Interestingly, mutants that lacked the ability to suppress K-Rta transactivation were still capable of complementing oriLyt-dependent DNA replication, indicating that this activity does not contribute to the DNA synthesis-related activity of K-bZIP.