GCaMP7a is a genetically encoded fluorescent Ca[2+] indicator. It is a fusion protein composed of an N-terminal 35 residue RSET leader sequence (which includes Tag:polyHis), the calmodulin-binding peptide M13, a circularly permuted green fluorescent protein based on EGFP and calmodulin. It was derived from GCaMP-HS, containing thirteen additional amino acid substitutions (PMID:23375894).