FIGURE 6.
Effect of the D302A and H305A substitutions on procapsid stability. A, the ability of procapsid to undergo the expansion that occurs upon capsid maturation was assessed by heating procapsids for 15 min at different temperatures. Expanded heads (ExH) run more slowly on agarose gels because of their larger diameters compared with procapsids (PC). B, stability of capsids to urea denaturation. Apparent midpoints for urea denaturation (Cm) from fits of the pseudo-equilibrium data to a six-parameter model (45) were are as follows: WT, 5.2 ± 0.1 m; D302A, 5.0 ± 0.2 m; H305A, 5.4 ± 0.1 m. Based on duplicate experiments the uncertainties in the Cm values are ∼0.2 m urea.