At the time of DNA extraction, FerrM cells, expressing mCAT-1, showed no cytopathic response and the observed level of unintegrated viral DNA was low (4.0% of M. dunni, Fig. 3A ,B). In contrast, virus-induced syncytia were observed in all 3 dCAT-1 transfectants. 2 of these 3 transfectants had large multinucleated syncytia that involved >50% of the cells in infected cultures (Fig. 3C) ; levels of unintegrated linear DNA in these cells were high (53% and 68% of M. dunni) (Fig. 3A,B) . The third dCAT-1 transfectant showed fewer and smaller syncytia ( dCAT-1-g : : : : V : : : : : : : : E : : : : : V : : : : : : G : : : :