Formation of the B1 core was probed by six mutations: H1, V103A; H5, V162A, L165A; and H6, V173A, L176A, V177A. The extent of helix formation was probed by six Ala to Gly mutations: H1, A98G, A102G; H5, A166G, A167G; and H6, A175G, A178G.