Structural elements of the 50 S subunit of E. coli ribosomes.

The large (50 S) subunit from E. coli ribosomes consists of 32 different proteins and two RNA molecules of different length. In an attempt to determine the three-dimensional arrangement of the proteins in the subunit, we are also interested in obtaining direct information on the shape of the proteins within the subunit. This is possible only with ribosomal subunits which, unlike natural protonated subunits, are homogeneous for neutrons. These homogeneous particles are produced by reconstituting 50 S particles from RNA and proteins isolated from bacteria grown at different levels of D2O in the culture medium, 76% D2O for RNA and 84% D2O for proteins. Model calculations and test experiments reveal that the pursued strategy allows direct determination of radii of gyration of 50 S components within the particle with reasonable precision. Data evaluation and interpretation are significantly facilitated by contrast variation of the reconstituted particles. The determination of protein shape parameters is only one aspect of the new strategy. The pair distance measurements are completely independent of its success. Data on radii of gyration of five ribosomal proteins in situ are reported: L1 (26 +/- 2 A), L2 (22 +/- 2 A), L3 (22 +/- 2 A), L4 (20 +/- 2 A), and L23 (13 +/- 2 A).