FIG 4.

Single-step growth curve of recombinant hMPVs carrying mutations in the SAM binding site. LLC-MK2 cells in 35-mm dishes were infected with each recombinant hMPV at an MOI of 0.01. After adsorption for 1 h, the inocula were removed and the infected cells were washed 3 times with Opti-MEM medium. Then, fresh Opti-MEM medium containing 2% FBS was added and the cells were incubated at 37°C for various times. Aliquots of the cell culture fluid were removed at the indicated intervals. The viral titer was determined by an immunostaining assay in Vero E6 cells. DPI, day postinfection. (A) Growth curves for wild-type rhMPV and the rhMPV G1696A, G1700A, and D1755A mutants; (B) viral titers for wild-type rhMPV and the rhMPV D1755A mutant at different MOIs.