The human AbetaH-J-J locus is a genomic sequence which generates three 
functionally distinct proteins, the enzyme aspartyl-beta-hydroxylase (AbetaH), 
the structural protein of sarcoplasmic reticulum junctin, and the membrane-bound 
calcium binding protein junctate. The first and second exons are mutually 
exclusive when mature mRNAs are produced. Moreover, the use of different splice 
donors has been shown to be involved in the generation of protein diversity by 
alternative splicing. As to transcriptional regulation, two promoters (P1 and 
P2) were identified. When the P1 and P2 promoter sequences are compared, 
important differences are clearly detectable. The most interesting result 
emerging from studies focused on the P2 promoter is that the calcium-dependent 
transcriptional factor MEF-2 activates the transcription of junctin, junctate, 
and AbetaH in excitable tissues and, to a lesser extent, in kidney. No Sp1 
binding sites are present in the P2 promoter. In contrast, P1 promoter contains 
GC-rich sequences, which have homologies with the Sp1 consensus binding site.