Phosphorylation at Serine 21 in G protein-coupled receptor kinase 1 (GRK1) is required for normal kinetics of dark adaption in rod but not cone photoreceptors.
Kolesnikov AV, Chrispell JD, Osawa S, Kefalov VJ, Weiss ER. FASEB J. 2020 Feb; 34(2):2677-2690. Epub 2019 Dec 30.