Arrestin (or S-antigen) [1] is a protein that interacts with light-activated phosphorylated rhodopsin thereby inhibiting or 'arresting' its ability to interact with transducin. In mammals, arrestin is associated with autoimmune uveitis.

Arrestin belongs to a family of closely related proteins including:

• β-arrestin-1 and -2, proteins that regulate the function of β- adrenergic receptors. They bind to the phosphorylated form of the latter thereby causing a significant impairment of their capacity to activate G(S) proteins.
• Cone photoreceptors C-arrestin (arrestin-X) [2], which could bind to phosphorylated red/green opsins.
• Phosrestins I and II from Drosophila and related insects. These proteins undergo light-induced phosphorylation and play an important role in photoreceptor transduction.

Sequence comparison of proteins from the arrestin family shows a high level of conservation. As a signature pattern, we selected a region located in the N-terminal section that contains many charged and hydrophobic residues.