Potassium ion (K+) channels are essential for a variety of cellular functions in both excitable and non-excitable cells and are likely to be involved in the pathogenesis of some cardiovascular and neurological disorders. To be useful in candidate gene analysis of inherited diseases it is important to identify new K+ channel genes and localize these sequences on the human physical and genetic maps. Using fluorescence in situ hybridization (FISH), we mapped two new K+ channel gene containing cosmids, c2-3a and c9-2a, to chromosomes 1 and 19, respectively. Partial DNA sequencing (c2-3a) and restriction enzyme site analysis (c9-2a) established the uniqueness of each clone. We refined the localization of c2-3a, c9-2a and a previously described K+ channel gene KCNA5, (c7-2), by performing contour length measurements of hybridized metaphase chromosomes and determining the average FLpter value (fractional length relative to the fixed reference point pter × 100). When compared to ideograms of banded metaphase chromosomes, these FLpter values correspond to 12p13.31→p13.33, 1p13.1→p21.1 and 19q13.32→q13.33, respectively. Using FISH, each of these clones has been finely mapped to a different human chromosome indicating a significant dispersion of K+ channel sequences in the human
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