FOLLOWING THE ASSEMBLY OF RNA-POLYMERASE DNA COMPLEXES IN AQUEOUS-SOLUTIONS WITH THE SCANNING FORCE MICROSCOPE

The capability of the scanning force microscope (SFM) to image molecul es in aqueous buffers has opened the exciting possibility of following processes of molecular assembly in real time and in near-physiologica l environments. This capability is demonstrated in this paper by follo wing the assembly process of RNA polymerase-DNA complexes. DNA fragmen ts deposited on mica and imaged in Hepes/MgCl2 are shown before and af ter Escherichia coli RNA polymerase holoenzyme is injected in the SFM liquid chamber. The protein can recognize and bind to these DNA fragme nts within several seconds after injection, suggesting that the protei n and the DNA retain their native configuration after deposition and d uring SFM imaging. A time lapse sequence depicting the process of asse mbly of RNA polymerase-DNA complexes is shown. These results represent the first step for acquiring the capabilities to monitor complex biom olecular processes as they take place in ionic solutions and to charac terize their spatial organization.