Difference of Fine Structure between Closed and Open Forms of Escherichia coli 30S Ribosomal Small Subunit by Negative Staining

Structures of ribosomal small subunits off. coll are classified into an open and a closed form, these forms changing one into the other reversibly when sub-jected to thermal treatment. The open and closed form particles have four and three typical lateral images, respectively. Interconversions are confirmed by the tilting experiment. The open form particle has two characteristic obli-quely extended arms, but the closed form particle has a simple ellipsoidal structure. Electron micrographs suggested that the two arms of the open form are folded in the large lower part of a closed form. As a result, it is suggested that both a closed form and an open form are meaningful structures of small subunits in the resolution of the three-dimensional reassociation process