What is an Aequorin?

Aequorin is a calcium-activated photoprotein isolated from the hydrozoan Aequorea victoria. Though the bioluminescence was studied decades before, the protein was originally isolated from the animal by Osamu Shimomura. In the animals, the protein occurs together with the green fluorescent protein to produce green light by resonant energy transfer, while aequorin by itself generates blue light.

Discussions of "jellyfish DNA" to make "glowing" animals often refer to transgenic animals which express the green fluorescent protein, not aequorin, although both originally derived from the same animal.