Genomic structures of synaptotagmin II protein: Comparison of exon-intron organization of the synaptotagmin gene family

Synaptotagmin (Syt) I (or II) is thought to be a Ca²⁺ sensor for neurotransmitter release in the rostral (or caudal) region of the mammalian brain. In this study, we first report the genomic structures and the transcription initiation site of the mouse syt II gene. Syt II protein coding regions consist of 8 exons with a total size of about 7 kbp. Exon 2 encodes the transmembrane domain, and exons 3-5 and 6-8 encode the C2A and C2B domains, respectively, although the precise intron positions within the two C2 domains are different. The syt II gene structures are quite similar to the mouse syt VIII and human syt IX genes, but not Caenorhabditis elegans syt I, human syt VII, or the mouse syt III genes, indicating that the exon-intron patterns of the functional domain of synaptotagmins (especially the C2A domain) have not been as well conserved during evolution as among isoforms. The only conserved feature among the synaptotagmin gene family seems to have a single exon that encodes the whole transmembrane domain. (C) 2000 Academic Press.