Connexin 35: A gap-junctional protein expressed preferentially in the skate retina

We have used low stringency hybridization to clone a novel connexin from a skate retinal cDNA library. A rat connexin 32 clone was used to isolate a single partial clone that was subsequently used to isolate seven more overlapping clones of the same cDNA. Two clones containing the entire open reading frame have a consensus sequence of 1456 bp and predict a protein of 302 amino acids length and molecular mass of 35,044 daltons, referred to as connexin 35 or Cx35. Southern blot analysis suggests that the cloned sequence lies in a single gene with one intron. Polymerase chain reaction amplification from genomic DNA and partial sequencing of this intron showed that it was approximately 950 bp in length, and located within the coding region 71 bp after the translation start site. Hydropathy analysis of the predicted protein and alignments with previously cloned connexins indicate that Cx35 has a long cytoplasmic loop and a relatively short carboxyl terminal tail. Multiple sequence alignments show that Cx35 has similarities to both alpha and beta groups of connexins and suggests that its origins may be near the divergence point for the two groups. Consensus sequences consistent with sites for phosphorylation by protein kinase C and by cAMP- or cGMP-dependent protein kinase were identified. Two transcripts were detected in Northern blot analysis: a 1.95-kb primary transcript and a 4.6-kb minor transcript. In RNA samples from 10 tissues, transcripts were detected only in the retina.