Human L-type Ca2+ channel α(1c) subunit gene (CACNL1A1) maps to the distal region of chromosome 12p13, and is composed of ≃ 50 exons spanning over 150 kb of the human genome as estimated by restriction map analysis. However, the structure and the total length of the 3'-end of the gene is not clear because the size of several big introns remains unknown. Here the fiber-FISH technique was used to determine the relative order and size of eight partial genomic DNA clones from the central and 3'-terminal regions of CACNL1A1. The total physical distance of this region, including the size and gap distances between the clones were re-estimated. The results show that the physical order of the tested clones was 5'- g14-5 > g12-2 > g10-8 > g4-5 > g16-7 > g8-3 > g12-5 > g6-20-3'. Their individual sizes vary between 6.7 and 21.9 kb. Clones g6-20 and g12-5, both containing repetitive exon 45/46-like element, were found to be located within 59.1 kb downstream of g8-3 containing earlier identified polyadenylation site, i.e. 229.5 kb away from clone g14-5 (exons 10, 11). The possible implications of this structural complexity is discussed.
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