Figure 1.

Scheme for observing nascent RNA in living cells. The approach is based on the high affinity binding of bacteriophage coat protein (i.e. MS2) to hairpins in the nascent RNA. Each stem loop binds a dimer of the coat protein, and each coat protein is labeled with a fluorescent protein (i.e. GFP). A) 5’ UTR labeling. When stem loops are located in the 5’ UTR, it is possible to visualize the RNA shortly after elongation commences. Here, three nascent RNAs are visible, resulting in a signal which is three times brighter than a single RNA. B) 3’ UTR labeling. When stem loops are located in the 3’ UTR, the nascent RNA is only visible once the polymerase proceeds to the end of the gene. Here, only a single nascent RNA contributes to the fluorescence signal.