The tightly regulated copper window in yeast.

The two opposing yeast copper regulators, Ace1 and Mac1, were converted into two fluorescent probes, Ace1-FRET and Mac1-FRET, which selectively and sensitively respond to Cu(+). The Cu(+)-binding curves obtained for both regulators as well as for the copper storage proteins Cup1 and Crs5 show that free copper(i) is maintained in a narrow window inside yeast.