Phenоtype is determined, in pаrt, by which genes аre expressed. The diаgram belоw illustrates hоw the product of gene X regulates the expression of other genes. At the top of the figure is a rectangle in which the middle 60 percent is unshaded, and each end is shaded. The rectangle is labeled “Gene X.” An arrow points from Gene X to a squiggly line with an arrowhead labeled “3 prime” at one end. The other end of the line is labeled “5 prime.” Another arrow leads from the squiggly line to a coiled line labeled “Protein X.” Shown below Protein X are four rectangles, each of which is unshaded in the middle and shaded at each end. From left to right, the rectangles are labeled “Gene 1,” “Gene 2,” “Gene 3,” and “Gene 4”. Arrows point from Protein X to Gene 1, Gene 2, and Gene 4, and the Protein X symbol is superimposed on the left shaded area of Gene 1, Gene 2, and Gene 4. Arrows point from Gene 1, Gene 2, and Gene 4 to squiggly lines below each of the genes. Each of the squiggly lines has an arrowhead labeled “3 prime” at one end. The other end of each line is labeled “5 prime.” Nothing is present below the rectangle labeled Gene 3. Which of the following statements best explains how protein X regulates gene expression?