The structure of CACNA1G, the gene encoding alpha1G, a human brain T Ca2+ channel alpha1 subunit, was determined by comparison of polymerase chain reaction-amplified brain cDNA and genomic sequences. The gene consists of at least 38 exons, two of them newly-identified, spanning at least 66490 basepairs of chromosome 17q22. Alternative splicing of the RNA occurs at six sites: cassette exons 14, 26, 34 and 35, an internal donor in exon 25 and protein-coding intron 38B. Additionally, the RNA can be polyadenylated at either of two sites. Alternative splicing of CACNA1G RNA may lead to expression of as many as 24 distinct protein products, ranging from 2171 to 2377 amino-acids residues.