A method for imaging E. c o l i. RNA polymerase holoenzyme with the scanning tunneling microscope in an aqueous environment

An electodeposition method has been developed for depositing E. coli. RNA polymerase onto a monoatomically flat gold surface. The scanning tunneling microscope has been used to image this enzyme in a high-humidity or water/glycerol environment, which allows direct observation without metal coating. The deposition technique is reproducible enough to allow optimization of the deposition parameters for controlled electrodeposition. Time-dependence studies were conducted to help determine the binding mechanism of the protein. The enzyme molecules appear as ordered arrays, amorphous features, or ‘‘jaw-shaped’’ molecules depending on the deposition conditions used. The ‘‘jaw-shaped’’ molecules closely resemble those observed by electron microscopy. In some of these a groove 22 Å wide can be seen.