Rapid movements of living biomolecules visualised

Dutch researcher Chris Molenaar has made the rapid movements of proteins, DNA and RNA molecules visible in living cells. With this technique researchers can study the dynamics of biomolecules in their natural environment.

Molenaar developed a method which makes it possible to follow the movements of RNA molecules in living cells. The researcher also made the movements and interactions between proteins in living cells visible with the aid of the revolutionary “Green Fluorescent Protein”.

Much of the present knowledge about molecular compositions of the cell and the mechanisms in which biomolecules such as DNA, RNA and proteins play a role, is based on experiments in tests tubes with biomolecules isolated from cells. However, with these molecules it is difficult to simulate the behaviour in a living cell. Dynamic processes in the cell can only be understood with living cell microscopy.

Molenaar used fluorescent probes which specifically bind to the molecule he wanted to study. By using a fluorescent microscope to examine where a fluorescent molecule was at different times, the movement of the structures containing these molecules could be followed. For example, the researcher followed the tips of chromosomes (telomeres) in three dimensions over the course of time.

The mobility of populations of molecules was visualised using FRAP (Fluorescence Recovery After Photobleaching). The fluorescent molecules in a small part of the cell are destroyed when a laser is focussed on them. However, although it no longer fluoresces, the biomolecule to which the fluorescent molecule is attached remains intact. The rate at which the fluorescent molecules from the surroundings move into this dark area says something about the mobility of, for example, a certain type of RNA or protein. This mobility in turns provides further information about the functioning of the molecules.

In addition to the movement of the biomolecules, Molenaar also visualised the interaction of different biomolecules. For this he used FRET microscopy (Fluorescence Resonance Energy Transfer). When two fluorescent molecules approach to within several nanometres of each other, one molecule can transfer energy to the other. This energy transfer causes a change in the colour of the fluorescence. Molecular interactions occur within distances of several nanometres. This distance cannot be resolved with a normal light microscope.

For further information please contact Dr Chris Molenaar (Department of Molecular Cell Biology, Leiden University Medical Center), tel. 31-71-527-6278, e-mail: c.molenaar@lumc.nl. The doctoral thesis was defended on 18 June 2003. Dr Molenaar’s supervisor was Prof. H.J. Tanke.

Image at www.nwo.nl/news. A short film can also be found in which it can be seen how a fluorescent probe specifically binds to the desired biomolecules (RNA) immediately after being injected into a living cell.

The research was funded by the Netherlands Organisation for Scientific Research.