Alignment of S2 and S3 sequences from Shaker, the Kv1.2/Kv2.1 chimera, Drosophila eag, and rat CNG4 (A) (Tempel et al., 1987; Warmke et al., 1991; Chandy and Gutman, 1995; Nelson et al., 1999; Long et al., 2007). Acidic residues conserved throughout the voltage-gated channel superfamily are shown in bold; positions of acidic residues conserved only in the eag and CNG subfamilies are underlined and shown in bold italics. The asterisk (*) above the conserved proline in S3 indicates the division between S3a and S3b (Alabi et al., 2007). Numbers corresponding to the Shaker and eag sequences are provided above and below the alignment, respectively. (B) Cartoon of the membrane topology of a voltage-gated K⁺ channel subunit shows the approximate locations of the binding site residues (filled circles) (Silverman et al., 2000). Circled negative signs indicate positions occupied by acidic residues throughout the voltage-gated channel superfamily (Chandy and Gutman, 1995). Circled positive signs indicate charge-moving arginine residues in the S4 segment (Aggarwal and MacKinnon, 1996; Seoh et al., 1996). Filled circles indicate positions occupied by acidic residues only in the eag and CNG channel subfamilies (Kaupp et al., 1989; Dhallan et al., 1990; Warmke and Ganetzky, 1994).