Structure and analysis of the transducin beta 3-subunit gene, a candidate for inherited cone degeneration (cd) in the dog

The cDNA for the beta 3-subunit of cone-specific transducin (T beta 3) was cloned and characterized from wild type dogs, and used in linkage studies as a candidate gene for cone degeneration. Sequence analysis of the T beta 3 cDNA revealed an open reading frame, of 1020 bp, potentially coding for a protein of 340 amino acids (aa). The deduced aa sequence of canine T beta 3 shares 97% identity with the previously identified human T beta 3, and 82% identity with bovine rod-specific transducin (T beta 1). RT-PCR and sequencing of the amplified products demonstrated that the retinal canine T beta 3 gene is expressed in two different transcripts which can be generated by alternative splicing of the intron in the 3'-untranslated region (UTR). The short and the long mRNAs differ in the length of their 3'-UTR by 456 nt. We have also determined the genomic organization of the canine T beta 3 gene; it consists of ten exons and the first exon is in the 5'-UTR. The cDNA encoding T beta 3 from c0d-affected dogs was also cloned and sequenced. We found no differences at the nucleotide level between the cDNAs isolated from normal and diseased retinas. The level of transcription of T beta 3 mRNA in the cd dog retina appeared to be normal. Linkage analysis of a crossbred informative pedigree showed five obligate recombinants out of nine informative offspring. These results suggest that T beta 3 is not a candidate gene for the cone degeneration of the cd mutant. (C) 1997 Elsevier Science B.V.