Identification of a missense mutation in the cytoplasmic domain of Kcc1. (A) Fine SNP mapping of 55 mice at 10 SNP markers localized in the RBC10 mutation between 105.92 and 109.15 Mb on chromosome 8. Light gray, homozygous for BALB/c; dark gray, heterozygous for BALB/c and C57BL/6; black, homozygous for C57BL/6. (B) DNA sequence results showing the T to A base substitution of Kcc1. (C) Quantitative reverse transcriptase-PCR for Kcc1 mRNA expression in the spleen. Mean ± SD for 3 age-matched mice of each genotype. (D) Schematic of Kcc1 protein showing the M935K mutation. (E) The M935 residue and adjacent amino acids display significant homology across vertebrate evolution, and (F) the human and mouse KCC family members.