Two gap junction genes, connexin 31.1 and 30.3, are closely linked on mouse chromosome 4 and preferentially expressed in skin

Two new gap junction genes isolated from the mouse genome code for connexin homologues of 271 and 266 amino acids, designated here Cx31.1 and Cx30.3, respectively. The two open reading frames, oriented in the same direction, are only 3.4 kb apart on mouse chromosome 4. Within the connexin family, these two proteins are most closely related to one another (70% amino acid sequence identity) and to Cx31 (65 and 68% identity, respectively). Comparison of the Cx31.1 mouse gene with a Cx31.1 cDNA showed a similar genomic organization to that found with other members of the connexin gene family, i.e. the coding and 3'-untranslated regions are contained within a single exon, which is preceded by an intron, less than 25 bases upstream of the ATG start codon. Northern blot hybridization revealed highly tissue-specific coexpression of the 1.6-kb Cx31.1 mRNA and two Cx30.3 transcripts of 1.9- and 3.2-kb size, predominantly in skin and two related mouse keratinocyte cell lines. Minor levels of Cx31.1 mRNA were detected in testis. Microinjection of Cx30.3, but not Cx31.1 cRNA, into Xenopus oocyte pairs induced formation of functional gap junction channels with unique voltage-gated parameters compared to other connexins expressed similarly.