Molecular cloning of mouse connexins26 and -32: similar genomic organization but distinct promoter sequences of two gap junction genes.

Connexins26 and -32 are subunit proteins of gap junctions that are coexpressed in hepatocytes and several tissues but individually expressed in other cells. Molecular cloning of both corresponding mouse genes revealed similar genomic organization, i.e., each gene consists of two exons with the complete coding region located in the second exon. The first exon of each gene is preceded by a TATA-less promoter region. The promoter of the mouse Cx26 gene has at least two transcription start sites and is located in a very GC-rich region which is reminiscent of promoters of house-keeping genes. Putative consensus sequences for a metal response element, the transcription factor NFkappaB, and several GC-boxes were found within 600 bp upstream of the Cx26 transcription start sites. The promoter region of the mouse Cx32 gene contains two putative binding sites for the transcription factor HNF-1 and consensus motifs for NF-1 as well as NFkappaB within 680 bp upstream of the main transcription start site. Thus the sequence comparison of mouse Cx26 and Cx32 promoter regions provides hints for possible consensus elements that could control individual expression as well as common regulation of these gap junction genes in various tissues. Cx26 mRNA is much more abundant in adult mouse skin than in adult kidney and liver where Cx32 transcripts are relatively strongly expressed.