The gene for retinal S-antigen (48-kDa protein) maps to the centromeric portion of mouse chromosome 1 near Idh-1.

S-antigen (48-kDa protein) is a soluble protein of the retina and the pineal gland that is believed to play an important role in the visual process. S-antigen is involved in the regulation of the activity of rod photoreceptor-specific cGMP-phosphodiesterase (cGMP-PDE). The activity of this enzyme has been shown to be deficient in the retina of the rd mouse, which is affected by an autosomal recessive disease characterized by degeneration of the photoreceptor cells. The abnormal cGMP-PDE activity could result from, among other things, a lesion in the enzyme itself or in any of the proteins that regulate it, such as the S-antigen. We have used a mouse cDNA clone for the S-antigen to map the corresponding gene, Sag, to mouse chromosome 1 near Idh-1. Since the rd gene is located on mouse chromosome 5, our results suggest that Sag is not the site of the rd mutation.