Palo Alto Institute of Molecular Medicine, Mountain View, CA 94043, USA.
Fifteen years ago, when the genes for the photosynthetic light-harvesting proteins were
found, my colleagues in molecular biology asked the following question: Why can't we use
these proteins as in vivo fluorescent tags, and wouldn't that be a lot better than
attaching ß-galactosidase to proteins and having to supply substrate for
visualization? The answer was straightforward: Sure, but the light-harvesting
proteins need associated pigments for their signal. You'll also have to express and
regulate 20 other genes for pigment biosynthesis. Green fluorescent
protein (GFP) gets around this problem by autocatalytically forming a fluorescent pigment
from natural amino acids present in the nascent protein. GFP works across the
phyla-from glowing tobacco mosaic virus with GFP- infected leaves to lighted sensory
neurons in worms. To these add fluorescent zebrafish eyes, flies, yeast, and yes,
possibly people- if engraftment with GFP-tagged stem cells in bone marrow becomes
possible.