 The RH domain is composed of alpha-helical region formed from the amino terminal sequence plus a short stretch of sequence following the kinase domain that provides 2 additional helices, and makes extensive contacts with one side of the kinase domain.Modeling and mutagenesis suggests that the RH domain senses GPCR activation to open the kinase active site.GRK1 is involved with rhodopsin phosphorylation and deactivation in vision, together with arrestin-1, also known as S-antigen.