Fig. 1. The structure of Kch, a subunit of the putative K⁺ channel in E.coli. (A) Membrane topology of a Kch subunit is composed of a channel body (S1–S6, cylinder) with a pore region between S5 and S6, and a RCK domain (M240–N393) (Jiang et al., 2001) after S6. M240 also initiates the production of RCK protein (see Figure 6A). (B) Sequence alignment of the pore region from selected K⁺ channels with the conserved K⁺ signature sequence (GYG) highlighted in gray. Kch, E. coli (NCBI protein database code GI: 11354242); Shaker, Drosophila melanogaster (GI: 13432103); KcsA, Streptomyces lividans (GI: 8134524); MthK, Methanothermobacter thermautotrophicus (GI: 21542150); Kat1, Arabidopsis thaliana (GI: 421842); eag, Drosophila melanogaster (GI: 399253); Herg, Homo sapiens (GI: 7531135); Irk1, Mus musculus (GI: 6680530); mSlo1, Mus musculus (GI: 6754436).