Luminescence resonance energy transfer analysis of RNA polymerase complexes

Resonance energy transfer allows measurement of atomic-scale distances under a variety of solution conditions. Luminescence resonance energy transfer (LRET) is a variant of energy transfer measurement in which lanthanide chelates are used as the probes. The unusual properties of lanthanide emission, in particular their long microsecond-scale lifetimes, offer several advantages for energy transfer measurements with biological samples. One of the unique features of LRET is the ability to measure energy transfer under conditions where severe heterogeneity of labeled macromolecules exists. This feature of LRET is the special emphasis of this article. We describe here LRET methodology with a particular attention to using sensitized acceptor emission to determine efficiency of energy transfer. Although we employed this technique in the characterization of Escherichia coli RNA polymerase complexes it is readily compatible with the study of essentially any protein.