CLONING AND CHARACTERIZATION OF A HUMAN DELAYED RECTIFIER POTASSIUM CHANNEL GENE

A human genomic DNA library was screened for sequences homologues to the rat delayed rectifier K(v) 2.1 (DRK1) K+ channel cDNA. Three phages were isolated which hybridized to K(v) 2.1 cDNA probes. Alignment of the human genomic DNA sequence with the rat cDNA sequence indicated that the open reading frame (ORF) is interrupted by a large intervening sequence, that separates exons encoding the membrane spanning core region of the K+ channel polypeptide. The K(v) 2.1 gene occurs once in the human genome and has been mapped to chromosome 20. The human, mouse and rat K(v) 2.1 proteins have been highly conserved, showing only a few substitutions outside of the membrane spanning domains in the amino- and carboxy-terminal cytoplasmic domains. Nevertheless, expression of human DRK1 channels in Xenopus oocytes showed that mouse, rat and human K(v) 2.1 channels have distinct pharmacological and electrophysiological properties. The observed differences in activation, voltage-dependence, 4-aminopyridine sensitivity and single-channel conductance have to be attributed to amino acid substitutions in the amino and/or carboxy-terminal cytoplasmic domains. Obviously, these domains of K(v) 2.1 channels influence biophysical K+ channel properties, which are thought to be determined solely by the membrane spanning core domain of potassium channels.