Figure 1: Transmembrane topology of the α 1C subunit. To illustrate the sites of molecular diversity, the polypeptide sequence is schematically segmented according to the CACNA1C genomic map [14] and the corresponding invariant (black) and alternative (blue) exons are outlined by black bars and numbered (1–50). Four regions of homology (I–IV), each composed of 6 transmembrane segments (numbered), are believed to be folded around the central pore. α-interaction domain (AID) of a constitutive β-binding site is shown in green. LA and IQ motifs (red) constitute calmodulin-binding domain (CBD).