When one is detecting nucleic acids by hybridization, there are numerous situations in which it is not desirable to isolate probe-target complexes from the excess of probes that are used. Sanjay Tyagi and Fred Russell Kramer, scientists at the Public Health Research Institute, N. Y., developed a new class of probe to be used just for those types of applications. Termed "molecular beacons," these single-stranded oligonucleotide probes can be used to report the presence of specific nucleic acids in solution. These probes can monitor nucleic acid synthesis in real time, without interrupting the reactions, and can be used to locate specific RNAs within living cells without killing the cells. Molecular beacons are hairpin-shaped ("stem-and-loop") molecules with an internally quenched fluorophore. They are "dark" when free in solution. Fluorescence is restored upon binding to the target nucleic acid.
The loop portion of a molecular beacon is a probe sequence complementary to ...
