SOLUTION SCATTERING STRUCTURAL-ANALYSIS OF THE 70-S ESCHERICHIA-COLI RIBOSOME BY CONTRAST VARIATION .1. INVARIANTS AND VALIDATION OF ELECTRON-MICROSCOPY MODELS

Solutions of selectively deuterated 70 S Escherichia coli ribosomes an d of free 30 S and 50 S subunits were studied by neutron scattering us ing contrast variation. The integrity of the partially deuterated part icles was controlled by parallel X-ray measurements. Integral paramete rs of the entire ribosome, of its subunits and of the protein and rRNA moieties were evaluated. The data allow an experimental validation of the two most recent electron microscopy reconstructions of the 70 S r ibosome presented by the groups of J. Frank (Albany) and of M. van Hee l & R. Brimacombe (Berlin). For each reconstruction, integral paramete rs and theoretical scattering curves from the 70 S and its subunits we re calculated and compared with the experimental data. Although neithe r of the two models yields a comprehensive agreement with the experime ntal data, Frank's model provides a better fit. For the 50 S subunit o f van Heel & Brimacombe's model the fit with the experimental data imp roves significantly when the internal channels and tunnels are filled up. The poorer fit of the latter model is thus caused by its ''sponge' '-like structure which may partly bt clue to an enhancement of high fr equency contributions in some of the steps of the three-dimensional im age reconstruction. It seems therefore unlikely that the ribosome has a ''sponge''-like structure with a pronounced network of channels. (C) 1997 Academic Press Limited.