Passage VI

Gene expression in eukaryotes is controlled by regulatory DNA sequences (RSs). RSs determine whether, for a particular type of cell, the expression of a gene is turned on or turned off.

Figure 1 shows the coding region of Gene X and shows 3 RSs (RS1-RS3 ) that are thought to be associated with Gene X. Figure 1 also shows the known expression pattern of Gene X across 6 types of mammalian cells (cell types A-F).

Scientists did 2 experiments to study how RS1, RS2 and RS3 control the expression of Gene X in each of cell types A-F. In each experiment, they prepared GFP reporter genes. GFP is a protein that emits green light when viewed with a certain microscope. Reporter genes are DNA molecules that contain RSs of interest and the coding region for an easily detectable protein.

Experiment 1

GFP reporter genes that contained RS1-RS3 and the coding region for GFP were prepared (see Figure 2). The reporter genes were then transfected (delivered) into cells of each of cell types A-F. Then, 48 hr after transfection, the cells were viewed with the microscope to determine if the GFP reporter genes were expressed. Figure 2 also shows the expression pattern of the GFP reporter gene across cell types A-F.

Experiment 2

Experiment 1 was repeated except that 5 types of GFP reporter genes were prepared. Each type of reporter gene contained either 0, 1, or 2 of the RSs and the coding region for GFP (see Figure 3). Figure 3 also shows the expression patterns of the 5 types of GFP reporter genes across cell types A-F.

Figures adapted from Bruce Alberts et al., Moleceluar Biology of the Cell, 5th ed. @2008 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.