This domain is found in the extracellular portion of receptor-like proteins - such as serine/threonine kinases and adenylyl cyclases [1,2]. This is a ligand-binding domain that binds cytokinin (Matilla et.al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).

1: The CHASE domain: a predicted ligand-binding module in plant cytokinin receptors and other eukaryotic and bacterial receptors. Anantharaman V, Aravind L; Trends Biochem Sci 2001;26:579-582. PMID:11590000

2: CHASE: an extracellular sensing domain common to transmembrane receptors from prokaryotes, lower eukaryotes and plants. Mougel C, Zhulin IB; Trends Biochem Sci 2001;26:582-584. PMID:11590001