Transmission election microscopy of wild-type and mutant viral particles. TEM of late (fixed 48 hr post-transfection) wild-type and mutant particles were assessed and scored from multiple sections. Panel A: the wild-type virus displayed typical size and conical core morphology. Panel B: the SD2 deletion mutant showed diminished production of viral particles, with altered diameter and core morphology. Panel C: the SD2-A423G-E18G-G31K mutant showed restoration of proper core morphology. Panel D: the SD2-A423G-K197R-G49K mutant also showed restoration of core placement and morphology. Bar size is shown for each panel.