Primary structure, organization, and expression of the rat connexin45 gene

In the mammalian heart, the gap junction protein connexin45 (Cx45) has a characteristic spatiotemporal expression pattern and is involved in mediating the rapid spreading of the electrical impulse that precedes coordinated contraction. The aim of this study was to isolate and characterize the rat Cx45 gene and to investigate its expression pattern in various tissues and cell lines. The gene consists of four exons (termed E1a, E1b, E2, and E3), of which the complete protein-coding sequence as well as a small part of the 5' -untranslated region (5'-UTR) reside on E3. 5' -Rapid amplification of cDNA ends (5' -RACE) analysis demonstrated the existence of four transcripts, which all contained the same coding region (derived from E3) but differed in the composition of their 5'-UTR. Analysis of Cx45 RNA expression in various rat tissues and cultured cell lines revealed that the transcripts composed of either E1a, E2, and E3 (i.e., E1a/2/3) or of E1b, E2, and E3 (E1b/2/3) sequences are both ubiquitously expressed. Comparison of the rat Cx45 gene structure with its murine ortholog indicated both similarities and species-specific differences in Cx45 gene organization. These findings will allow for the mapping and characterization of the rat Cx45 gene regulatory regions.