Sequence and developmental expression of mRNA coding for a gap junction protein in Xenopus.

Cloned complementary DNAs representing the complete coding sequence for an embryonic gap junction protein in the frog Xenopus laevis have been isolated and sequenced. The cDNAs hybridize with an RNA of 1.5 kb that is first detected in gastrulating embryos and accumulates throughout gastrulation and neurulation. By the tailbud stage, the highest abundance of the transcript is found in the region containing ventroposterior endoderm and the rudiment of the liver. In the adult, transcripts are present in the lungs, alimentary tract organs, and kidneys, but are not detected in the brain, heart, body wall and skeletal muscles, spleen, or ovary. The gene encoding this embryonic gap junction protein is present in only one or a few copies in the frog genome. In vitro translation of RNA synthesized from the cDNA template produces a 30-kD protein, as predicted by the coding sequence. This product has extensive sequence similarity to mammalian gap junction proteins in its putative transmembrane and extracellular domains, but has diverged substantially in two of its intracellular domains.