Quaternary structure of the ribosomal 30S subunit: model and its experimental testing

In considering the structure of the 30S subunit of the Escherichia coli ribosome, we have assumed that: (i) all or almost all the proteins within the 30S particle are compact and globular, as recently shown for the isolated proteins S4, S7, S8, S15, and S16 in solution [Serdyuk, I.N., Zaccai, G. & Spirin, A.S. (1978) FEBS Lett. 94, 349-352]; (ii) the RNA within the 30S particle has approximately the same specific V-like or Y-like shape that was demonstrated for the isolated 16S RNA in a compact conformation [Vasiliev, V.D., Selivanova, O.M. & Koteliansky, V.E. (1978) FEBS Lett. 95, 273-276]. From these assumptions and using the numerous data reported on neighboring ribosomal proteins, we have constructed a model of the quaternary structure of the ribosomal 30S subunit. The model has been tested by calculation of the theoretical curves of neutron scattering at different contrasts, as well as those of x-ray scattering, and their comparison with the experimental scattering curves for E. coli 30S particles. It has been found that the calculated scattering curves for the model practically coincide with the experimental scattering curves for the 30S particles in the range of Bragg distances down to 40-55 A. The scattering curves calculated for several three-dimensional patterns of arrangement of the 30S subunit proteins proposed earlier have been shown to be inconsistent with the experiments.