Structure of the 50S ribosomal subunit from Escherichia coli. Investigation of the intact subunit and core particles by electron microscopy and analogue image processing.

Structures of 50S ribosomal subunits, CsCl and ethidium bromide core particles from these subunits have been investigated by electron microscopy and image processing by FAIRS. This method revealed structural details which are obscured in individual images, and enabled to distinguish six crown forms, different in their side protuberances, and two kidney forms. Crown forms were imaged as symmetrical or asymmetrical forms. The latter type was far more frequent in untreated populations than the first. The depletion of proteins by both agents caused stepwise degradation of the side protuberances in the crown forms thereby transforming asymmetrical to symmetrical forms. It is concluded from these findings that asymmetrical and symmetrical forms in untreated populations represent also structurally different particles. From the higher complexity in terms of component composition and structure it is concluded that the asymmetrical crown forms are more likely to represent the native structure of isolated 50S subunits than the symmetrical forms. Existing models for this subunit are discussed in terms of this finding.