Green fluorescent protein (GFP tag) is a ~27 kDa protein consisting of 238 amino acids derived from jellyfish Aequorea Victoria. GFP exhibits bright green fluorescent light when exposed to blue light. It has been used widely as a reporter protein for gene expression in eukaryotic and prokaryotic organisms, and as a protein tag in cell culture and multicellular organisms. Anti GFP-tag antibodies are often used in biological research and related fields. GFP tag antibodies are also often been used to study the expression of proteins and the interaction between proteins and proteins.