Structural conservation of the genes encoding CaT1, CaT2, and related cation channels

We report here the genomic structures of the genes encoding human calcium t ransport proteins CaT1 and CaT2, which belong to a recently identified clas s of highly selective calcium entry channels. The mRNA for CaT1 was express ed more abundantly than that for CaT2 in three major tissues involved in tr anscellular calcium transport, namely intestine, kidney, and placenta, as d etermined by quantitative PCR. The genes encoding CaT1 and CaT2, ECAC2 and ECAC1, respectively, are completely conserved in terms of exon size in the coding regions. They also share similar intron-exon structures with the gen es encoding the closely related, nonselective cation channels VRI, VRL-1, O TRPC4 (also known as VR-OAC, Trp12, and VRL-2), and a hypothetical protein, VRL-3. We conclude that ECAC2 and ECAC1, which encode calcium selective ch annels, share a common ancestral gene with the genes encoding the related n onselective cation channels.