Structure of a Beheaded 30 S Ribosomal Subunit from Thermus thermophilus

The 22S ribonucleoproten particles containing the 5′ (body) and the central (platform) domains of the Thermus thermophilus 30S subunit has been studied by sedimentation, neutron scattering and electron microscopy. The RNP particles have been obtained by oligonucleotide-directed cleavage of 16S RNA with ribonulease H in the region of the 900th nucleotide of the protein-deficient derivatives of the 30S subunits. It is shown that these RNP particles are very compact, though their form and dimensions differ slightly from those expected from the electron microscopy model of the 30S subunit beheaded by computer simulation. The particles are subdivided into two structural domains whose mutual arrangement differs from that of the corresponding morphological parts of the native 30S subunit. Electron microscopy demonstrates that the mutual arrangement of domains in the RNP particles is not strictly fixed suggesting that interaction with the third domain of the 30S subunit is a requisite for their correct fitting.