Cloning and sequence analysis of rat cystic fibrosis transmembrane conductance regulator

A complementary DNA (cDNA) encoding the rat cystic fibrosis transmembrane conductance regulator (CFTR) has been isolated and the tissue distribution of the rat CFTR mRNA has been determined. Northern blot analysis revealed that the highest levels of the 6.3 kilobase (kb) CFTR mRNA were expressed in the colon, with expression also noted in uterus, lung, stomach, and small intestine. A 7.5-kb mRNA was expressed in skeletal muscle, and in testes both the 7.5-kb mRNA and a 6.0-kb mRNA were expressed. Five cDNAs were isolated from a rat colon library, the longest corresponding to codons 684 through the poly A tail. Three other clones, corresponding to codons 213 through 245, 372 through 574, and 656 through 886 were also isolated. Polymerase chain reaction amplification of cDNA prepared from rat colon mRNA was utilized to clone the remainder of the cDNA. The predicted amino acid sequence of the rat CFTR is 79% identical to the human CFTR, with 73% identity noted in the R domain, and 81 and 83% identities noted in nucleotide binding folds 1 and 2, respectively. Thirty-two of the 38 potential phosphorylation sites identified in the human CFTR were also present in the rat CFTR.