Analysis of WT and mutants virion morphology. (A) Virus particles produced from 293T cells transfected with WT, S109A, S149A or S178A molecular clones were processed as described in "Materials and Methods" and imaged in thin-layer electron microscopy. Aberrant cores are indicated by an arrow. Identical scale is used for all images (scale bar = 60 nm). (B) Diameter distribution observed for WT and mutant viruses. Mean diameters are indicated.