The Putative Packaging <scp>ATPase</scp> of <i>Acanthamoeba polyphaga</i> Mimivirus Is an Essential Protein That Interacts With the Genome Segregation and Packaging Machinery

Giant viruses are hypothesized to utilize the FtsK/HerA type ATP-driven motor to package the genome during the virus assembly. Previously, we reported the presence of several recombinases and topoisomerase II in Acanthamoeba polyphaga mimivirus (APMV) that could potentially work in concert with the vaccinia virus (VV) A32-like packaging motor to facilitate segregation of the genome and its packaging in giant viruses. In the present study, we have identified the interaction network among the probable components of the APMV segro-packasome machinery, namely, two paralogous packaging motors, three paralogous recombinases, and a topoisomerase II using yeast two-hybrid and pull-down assays. Our data show that both copies of the packaging ATPase interact with topoisomerase type II, and interestingly, the network also includes all three copies of the serine recombinases, suggesting that these interactions may be essential for DNA processing before its packaging into the capsid. We also show that the gene encoding the packaging ATPase gene is essential for virus propagation. Although deletion of each of the three recombinases is not lethal, the progeny viruses show slightly reduced fitness, suggesting that they play an important role in virus assembly. Taken together, our data indicate that genome segregation and packaging mechanisms operative in some giant viruses exhibit many parallels to the mechanism of prokaryotic chromosome segregation during cell division.