Computer-averaged views of the 70 S monosome from Escherichia coli.

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.