Ratiometric-Pericam is a genetically encoded fluorescent Ca[2+] indicator. It is a fusion protein composed of the calmodulin-binding peptide M13, a circularly permuted green fluorescent protein and Xenopus calmodulin. The circularly permuted fluorescent protein is interrupted at residue 145 and is based on EYFP-Q69K, with the additional mutations H148D and T203F (PMID:11248055). For detailed kinetic and spectral properties, see PMID:11248055.