Helical arrays of Escherichia coli small ribosomal subunits produced in vitro.

In vitro conditions have been determined for obtaining ordered helical ribbons of small ribosomal subunits from Escherichia coli. These ribbons, suitable for study by three-dimensional reconstruction, are the first ordered arrays of ribosomes or ribosomal subunits to be produced in vitro.Although small ribosomal subunits remain in solution for extended periods (up to 6 months) during this procedure, their structural integrity, as assessed by acrylamide/agarose gel electrophoresis, by sucrose gradients, and by electron microscopy, is not significantly altered.Electron micrographs of ribbons of small subunits diffract to 60 Å resolution. Optical diffraction patterns suggest that adjacent subunits within helical ribbons are related by a 2-fold screw parallel to the long axis of the ribbon and the helical repeat distance measured from electron micrographs is 220 Å.