GINKO1 is a genetically-encoded fluorescent sensor for K[+]. It consists of the Escherichia coli kbp (K[+] binding protein) coding sequence inserted into the EGFP green fluorescent protein at residue 144. The BON and LysM domains of the kbp protein show K[+]-dependent association, resulting in a conformational change that increases fluorescence in the presence of K[+] (PMID:30652129).