aeq::GAP3 is a ratiometric low affinity Ca[2+] sensor that is optimized for measurements in high-Ca[2+] concentration environments. It is a fusion protein composed of a variant of the GFP fluorescent protein, a 16-residue linker and a mutant form of Avic\aeq that contains the mutations D24N and D119A to decrease the affinity to Ca[2+]. The GFP variant in GAP3 contains the Q80R, F99S, M153T, V163A mutations present in the original 'GAP1' Ca[2+] sensor (PMID:24501126), plus additional mutations (L15Q, I167V, S175G and D180Y) to increase the fluorescence intensity (FBrf0241114).