ABSTRACT
A ªuorescent protein (FP) was an unusual concept at that time, which naturally invited further investigation. It was found that GFP was encoded by a single gene, which was in due course sequenced. This was the beginning of a revolution in cell biology. GFP proved to be a very stable protein; its ªuorescence is unaffected by harsh conditions such as 8 M urea, 1% SDS, and 2 days’ treatments with various proteases; it also survives aldehyde Žxation. GFP is stable over a large range of pH (5.5 to 12) and at temperatures up to 65°C. Because it is so stable, is encoded by a single gene, needs no posttranscriptional modiŽcation, and requires no cofactors, GFP has revolutionized cell biology by providing an expressible marker that is directly visible in the ªuorescence microscope (ChalŽe et al., 1994; Inouye & Tsuji, 1994).
