MEMORY is not something you would normally associate with yeast cells, but with a genetic “circuit” inside them the cells can “remember” exposure to a molecule of the sugar galactose.
A team led by Pamela Silver at Harvard Medical School in Boston created the circuit to show that biological systems could be engineered in the same way as mechanical ones. They used the galactose to trigger expression of a gene, the product of which turned on a second gene. This gene then acted to turn itself on again and again, creating an .
So after the galactose triggers the circuit, the second gene stays activated indefinitely, regardless of whether galactose is still present. In Silver’s circuit, the second gene produces a fluorescent molecule, so the cells glow green if they have been exposed to galactose. The circuit stayed active for at least nine generations and possibly many more.
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The system could be used to flag up cells that have been exposed to a particular drug or suffered DNA damage, Silver says (Genes and Development, vol 21, p 2271).
