Genomic structure of a novel chloride channel gene, CLIC2, in Xq28.

A transcript map was previously constructed in the 1200-kb telomeric region of Xq28. One of the cDNAs, XAP121, displayed homology to a p64 bovine chloride channel and to a human chloride channel (p64CLCP, NCC27) at both the nucleotide and the peptide levels. In addition, all three sequences exhibited homologies to numerous ESTs derived from human, mouse, rat and pig. While the human NCC27 and XAP121 homologs encode small peptides of 241 and 243 amino acids, respectively, the bovine peptide has a length of 437 amino acids. This suggests that the human genes represent a novel and separate class of small chloride channels. Unlike other chloride channels, the NCC27 peptide was recently shown to localize intracellularly in the cytoplasm and nucleus. The NCC27 and XAP121 genes have thus been designated CLIC1 and CLIC2 for chloride intracellular channel genes 1 and 2, respectively. Since a direct association exists between a number of human chloride channel genes and a range of hereditary diseases, CLIC2 possibly represents a candidate for one of the many diseases linked to Xq28. To facilitate defined mutation analyses, we determined the genomic structure of the CLIC2 gene.