Ribosome structure: three-dimensional distribution of proteins S14 and S4

Single-particle applications at intermediate resolution

Electron microscopy together with single-particle image processing is an excellent method for structure determination of biological assemblies that exist in multiple identical copies. Typical assemblies contain several proteins and/or nucleic acids in a defined and reproducible arrangement. Coherent averaging of electron microscopic images of 5000-100,000 copies of these assemblies allows the determination of three-dimensional structures at ca. 1-3-nm resolution. At this intermediate resolution, it is possible to map individual subunits and thus to understand the architecture and quaternary structure of the assemblies. The intermediate resolution structural information gives a solid basis on which pseudo-atomic models of the assemblies can be modeled provided that high-resolution structures of smaller entities are known. The architecture of the assemblies, their pseudo-atomic models, and knowledge on their plasticity during function give a comprehensive understanding of large-scale structural dynamics of multicopy biological complexes. In this review, we will introduce the experimental pipeline and discuss selected examples.

The accessibility of antigenic determinants of ribosomal protein S4 in situ

Antibodies to Escherichia coli ribosomal protein S4 react with S4 in subribosomal particles, eg, the complex of 16S RNA with S4, S7, S8, S15, S16, S17, and S19 and the RI reconstitution intermediate, but they do not react with intact 30S subunits. Antibodies were isolated by three different methods from antisera obtained during the immunization of eight rabbits. Some of these antibody preparations, which contained contaminant antibodies directed against other ribosomal proteins, reacted with subunits, but this reaction was not affected by removal of the anti-S4 antibody population. Other antibody preparations did not react with subunits. It is concluded that the antigenic determinants of S4 are accessible in some protein deficient subribosomal particles but not in intact 30S subunits.

The 30 S subunit of the Escherichia coli ribosome. Topographical model of its component proteins

This topographical model of the proteins of the 30 S subunit of the Escherichia coli ribosome was built to be consistent with the 37 published spectroscopic and chemical experiments that indicate proximity and with the two neutron diffraction experiments that indicate S3 and S7 as well as S2 and S5 to be separated by 110 A. The model is quite consistent with the protein arrangement suggested by assembly pathways, the various RNA binding sites, and the streptomycin-associated proteins, This consistency is encouraging since none of these data were considered during the construction of the model. The model differs significantly from those proposed by Traut et at. ((1974) Ribosomes 271-308) and by Tischendorf et al. ((1975) Proc. Natl. Acad. Sei. U.S. 72, 4820-4824).