Rat pineal S‐antigen: Sequence analysis reveals presence of α‐transducin homologous sequence

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Abstract
S‐antigen (S‐Ag) is a soluble, highly antigenic protein, the administration of which induces autoimmune uveitis. This protein is found in the retina and pineal. Retinal S‐Ag from three species has been sequenced. In this study rat pineal S‐Ag was sequenced. Clones were isolated from a rat pineal λgt11 cDNA library by probing with a 300 bp fragment of mouse retinal S‐Ag cDNA containing the 5′‐coding region. The largest clone isolated (RPS‐118; 1364 bp) contained the entire coding sequence. Comparison of the rat pineal and mouse retinal S‐Ag nucleotide sequences indicated a high homology (95%). The deduced amino acid sequence was found to contain 403 residues (≌44 992 Da). Comparison of the rat pineal and mouse retinal S‐Ag amino acid sequences also revealed high homology (97%). The similarity of both the nucleotide and amino acid sequences of rat pineal and mouse retinal S‐Ag indicates that expression of the S‐Ag gene in both tissues is similar. Further analysis of the rat pineal S‐Ag sequence indicated that it contained essentially the same major uveitopathogenic region of S‐Ag present in bovine retina; minor uveitopathogenic sites were somewhat different. As is true of retinal S‐Ag, rat pineal S‐Ag contains the same consensus phosphoryl‐binding site present in many GTP/ GDP‐binding proteins and a homologous sequence found in the C‐terminus of α‐transducin. These sequences may play a role in the action of pineal S‐Ag in transmembrane signal transduction.