Primary structure of the canine CD4 antigen.

After PCR amplification two overlapping cDNA clones encoding the dog homologue of the human CD4 glycoprotein were identified. This internal fragment of the mature protein including the complete extracellular domains, consists of 1297 bp with a deduced amino acid sequence of 432 residues. The dog CD4 molecule differs from the corresponding protein of other species including human in the second domain. We found nine extra residues in the beginning of that domain, a cysteine at position 138, usually involved in a disulfide bridge, is substituted by tryptophan, and three new glycosylation sites are present.