RGS13 (Regulator of G Protein Signalling 13): RGS13 is a protein involved in regulating G protein-coupled receptor (GPCR) signalling. It plays a key role in modulating the signal transduction of specific hormones and neurotransmitters. RGS13 is especially important in immune cells such as mast cells and B cells, where it contributes to allergy and immune response regulation.