Figure 2.

Hydrophobic region S0 is an additional transmembrane region. (A) Autoradiogram of H-S0 and D-S0 proteins after in vitro translations, high pH treatment, separation into microsomal pellet (P) and soluble fraction (S), and SDS/PAGE. The apparent molecular weights of H-S0 and D-S0 are higher than the calculated molecular weights (H-S0, 12.5 kDa; D-S0, 14 kDa). This may be due to a stable secondary structure, which might also explain the diffuse bands. (B) PNGase F treatment of microsomal pellets of H-S0 and D-S0; + and − indicates treatment with and without PNGase F. (C) Proposed membrane topology of H-S0, D-S0, and HΔN43. MaxiK channels possess additional hydrophobic regions (S7–S10) at the C terminus that are shown as intracellular. We prefer this topology because of the relatively low hydrophobicity of these potential transmembrane regions. (D) Functional rescue of the N-terminal deletion clone HΔN43 by coexpression of H-S0. Oocytes were injected with 10 ng of HΔN43 cRNA alone or along with 5 ng of H-S0 cRNA and currents were measured in inside-out patches in 10 μM free Ca²⁺.