Fig. 1. The jShak1 channel lacks one acidic residue in S2 and one basic triplet motif in S4, compared with Drosophila Shaker and RatK_V1.2. (A)A schematic of a single 6TM alpha subunit of the Drosophila Shaker voltage-gated potassium channel. The S5-pore, S5-S6 loop and S6 domain are shown in grey and the S1-S4 transmembrane helices are white. The conserved acidic residues in S2 and S3 are labelled as are the characteristic basic residues in S4. (B)Alignments of the transmembrane helices S2, S3 and S4 in selected Drosophila, rat and hydrozoan K_V channels. The jellyfish (Polyorchis penicillatus) channel jShak1 lacks one (N227) of the two acidic residues in S2 but contains the stabilizing acidic residue (D260) in S3. The S4 voltage sensor of jShak1 lacks one basic motif found in other K_V1 channels but has the same helical length. The highly conserved acidic residues (E283 and E293) in S2 and the conserved acidic residue (D316) in S3 and the basic residues in the S4 voltage sensor of Drosophila Shaker and other Shaker-type channels are highlighted in grey. (C)Alignment of the S4 helix of jShak1 with the S4 helices of three other channels, indicating the sites of insertion of the S4 mutants used in this study on either side of position K294 (highlighted in black) in jShak1.