The discovery of green fluorescent protein and cloning of its gene from Aequorea victoria heralded a new era of investigation in virtually every field of cell and molecular biology ranging from the study of gene expression to protein sorting, organelle structure, measurement of protein-protein interaction, and so on.Before GFP, however several other fluorescent molecules has been in use but none of them could be as potential as GFP. What makes GFP so significant is its ability to fluoresces itself once formed in comparison of other bioluminescent molecules (such as aequorin and firefly luciferase) which require the addition of other substrate before they glow. Further, it is a small protein and can be attached to the protein of interest without disturbing its proper function. Also its small size allows following the fused protein, especially in organelles like neurons.