Metal-responsive transcription factors exist in yeast to modulate expr
ession of genes that encode proteins involved in cellular uptake of co
pper, iron and zinc ions. These signal transduction pathways function
in the cellular regulation of the intracellular concentration of free
metal ions. A second component of metal homeostasis is the regulation
of metal-ion binding through protein-mediated metallation. Copper-spec
ific chaperones exist in yeast that route copper ions to the site of b
iosynthesis of copper-metalloenzymes.