Helical whell representation of one subunit of the Kir family colored according to the results of mutagenesis experiments. (a) The side chains of Ml and M2 are colored according to the categories from the screening experiments of Minor et al. . [b] The side chains of M2 are colored according to the alanine and tryptophan scanning experiments of Choe et al. ; black tolerates both tryptophan and alanine, yellow tolerates alanine but not tryptophan, red tolerates neither alanine nor tryptophan.