Electron microscopy and image processing applied to the study of protein structure and protein-protein interactions.

We review the application of electron microscopy and image processing at the molecular level to an ever increasing range of biological specimens. Although recent advances have been due in part to development of more sophisticated instrumentation and/or processing algorithms, widespread application of the well-known techniques of image enhancement and structure reconstruction has depended on new strategies of in vitro crystallization and polymerization, some of which are outlined here. We also discuss the use of stoichiometric labeling and/or "cocrystallization" in identifying the different subunits in multisubunit complexes and in studying protein-protein interactions.