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Computer-averaged views of the 70 S monosome from Escherichia coli
Abstract:
The prokaryotic (70 S) monosome, composed of a roughly hemispherical 50 S large subunit and an elongate 30 S small subunit, appears in the electron micrograph in only a few common views representing the small number of preferred orientations assumed by the particle. Two of these, termed O and L views, have previously been characterized as the overlap and non-overlap projections; a third view, which we term the R view, represents the other endpoint of a rotational continuum with the overlap or O view. Tilt studies enabled us to calibrate this range as spanning approximately 50 degrees. The disjunct set of L views was averaged, and the reproducible resolution was determined to be 1/3.5 nm-1. The combined sets of O and R views were analyzed by correspondence analysis, and a continuous "rotation series" of subaverages was obtained. Interpretation of the views in the light of what is known about the morphologies of the individual subunits allows a general picture of the mutual fit of the subunits in the monosome to be conceived.
Insights
Researchers visualized the prokaryotic (70 S) monosome, revealing preferred orientations. This study provides insights into the structural arrangement and subunit interactions within this essential cellular particle.
Area of Science:
- Structural biology
- Molecular biology
- Biophysics
Background:
- Prokaryotic (70 S) monosomes consist of a 50 S large subunit and a 30 S small subunit.
- Electron microscopy reveals limited preferred orientations of monosomes, complicating structural determination.
Purpose of the Study:
- To characterize different views of the prokaryotic (70 S) monosome using electron microscopy.
- To determine the structural arrangement and subunit interactions within the monosome.
Main Methods:
- Electron microscopy with tilt studies to capture various particle orientations.
- Image analysis techniques including averaging and correspondence analysis.
- Resolution determination of averaged L views to 1/3.5 nm-1.
Main Results:
- Identified and characterized three common views (O, L, and R) representing a rotational continuum.
- Established a rotational series of subaverages for the O and R views.
- Achieved reproducible resolution for L views, enabling detailed structural interpretation.
Conclusions:
- A general model for the mutual fit of the 50 S and 30 S subunits within the prokaryotic (70 S) monosome was conceived.
- The study advances understanding of prokaryotic ribosome structure and orientation.
- Provides a framework for further structural investigations of monosomes.