These proteins are essentially ubiquitous, although they are not encoded within genomes of Haemophilus influenzae , Mycoplasma genitalium, and Mycoplasma pneumoniae .
Several organisms contain multiple ClC family paralogues.
For example, Synechocystis has two paralogues, one of 451 residues in length and the other of 899 residues. There are nine known members in mammals, and mutations in three of the corresponding genes cause human diseases. E. coli , Methanococcus jannaschii and Saccharomyces cerevisiae only have one ClC family member each. While one member of the family, Torpedo ClC-O, has been reported to have two channels, one per subunit, others are believed to have just one. All functionally characterized members of the ClC family transport chloride, some in a voltage-regulated process.