The Arabidopsis thaliana K + channel AKT1 was expressed in decreased K + content, and lower growth rate, as compared to control cells expressing the wild-type channel) were selected. a yeast strain defective for K + uptake at low K + concentrations ( B 3 mM). Besides restoring K + transport in this By co-expressing them with the wild-type AKT1 cDNA, it was strain, AKT1 expression increased its tolerance to salt (NaCl shown that the mutated polypeptides were expressed, stable and correctly targeted to the cell membrane where they or LiCl), whatever the external K + concentration used (50 mM, 5 mM, or 50 mM). We took advantage of the latter formed channels with altered properties. Analysis of the mutaphenomenon for screening a library of channels randomly tion distribution in these channels suggests that the AKT1 P mutated in the region that shares homologies with the pore domain has a structure similar to that of animal Shaker channels (a strongly constrained central region lining the forming domain (the so-called P domain) of animal K + tunnel that includes the highly conserved consensus motif channels (Shaker family). Cassette mutagenesis was performed using a degenerate oligonucleotide that was designed TXXTXGYGD, and flanking regions forming the outer mouth of the pore), with an additional selectivity filter located up-to ensure, theoretically, a single mutation per P cassette. The mean number of amino acid exchanges per cassette turned out stream from the tunnel and formed by residues present in the to be 1.4. Mutant channels that conferred on the transformed N-terminal flanking region. cells a reduction in salt tolerance (increased Na + content,