Question: Transcription factor X binds to a response element in gene A and gene B. In muscle cells, transcription factor X activates transcription of gene A. In neuronal cells, the transcription factor X activates transcription of genes A and B. In skin cells, transcription factor X activates transcription of only gene B. In liver cells, the same transcription factor prevents transcription of genes A and B. Remember that genes A and B and all their associated regulatory regions are present (and identical) in all three cell types – the genes are only differentially expressed in the three cell types! Draw a schematic of three cell types, each containing the two genes and their regulatory regions. Indicate response elements and regulatory proteins that are bound to the gene in each cell. Introduce new regulatory proteins as necessary to fit the scenario above. Use as few regulators as possible.