There are approximately 4000 DNA sites in the yeast genome which could potentially bind the yeast transcription factor GAL4, but only 10 sites control genes necessary for galactose metabolism.
In one chromatin immunoprecipitation experiment, yeast growing on galactose were lysed, and subjected to cross-linking reagents which cross-linked transcription factors to DNA. Next the DNA was sheared into small fragments, and antibodies to GAL4 were added. These antibodies coprecipitated the GAL4 and the DNA it was cross-linked to. The cross-linking was then chemically reversed, and the DNA was isolated and sequenced. Results showed that only 10 of the possible 4000 sites had GAL4 bound.
What eukaryotic gene control strategies would allow GAL4 to bind to the 10 sites and not bind to the 3990 other sites?