Yesterday’s first-year biology practical involved forcing the laboratory work-horse bacterium Escherichia coli to take up a circular piece of DNA called pGLO.

pGLO contains a few genes, but the most interesting of these DNA sequences encodes a protein from a jellyfish. This protein fluoresces green under UV light, and goes by the thoroughly unimaginative name of green fluorescent protein (GFP). The production of the GFP is regulated by a second DNA sequence, this time taken from a bacterium. The normal job of this regulatory DNA sequence is to switch on and off the production of enzymes that degrade an uncommon sugar called arabinose. Since bacteria don’t often encounter arabinose, the enzymes are not produced unless there is actually some arabinose around to eat. This save resources.