FIG 3.

M1 suppressor mutations complement the M2Y76A defect in filamentous particle budding. (A) rUdorn and rUd-M2Stop viruses with the indicated M1 suppressor mutations were used to infect MDCK-M2Y76A cells at a high MOI. rUdorn-infected MDCK cells (wild type) were used as a positive control for filament formation. Surface HA staining by immunofluorescence assay with anti-HA antibody (green) at 16 hpi was used to detect filamentous structures. NS1 (red) is shown to identify all virus-infected cells, and nuclei are stained with Hoechst stain (blue). The images were taken with an LSM 510 confocal microscope with a 100× objective. Independent experiments were done three times, and representative images are shown. (B) The percentage of infected cells showing viral filaments was quantified by counting total infected cells and cells possessing filaments in 20 independent fields per sample. The data are from one experiment and are representative of three independent experiments. Asterisks indicate statistically significant differences compared to rUd-M2Stop-infected M2Y76A cells (P < 0.01, one-way ANOVA with Bonferroni posttest). WT, wild type.