Assembly of ribosomal proteins L7, L10, L11, and L12, on the 50 S subunit of Escherichia coli.

We have determined the in vitro assembly sequence of ribosomal proteins L7, L10, L11, and L12 on Escherichia coli 50 S subunits by reconstitution experiments with the use of various ribosomal core particles and split protein fractions produced by treatment of 50 S subunits with 1 m NH4Cl and 50% ethanol. Proteins L7, L10, L11, and L12 were removed by a two-step treatment, first at 0 degrees, then at 37 degrees. Small amounts of proteins L1, L5, and L6 were also removed under these conditions. A one-step extraction of 50 S subunits at 0 degrees removed only proteins L7 and L12, while a similar one-step extraction of intact 50 S subunits at 37 degrees removed proteins L7, L12, and L10. Two-dimensional gel electrophoresis of the protein components and measurement of the ribosome-elongation factor G-guanosine diphosphate complex formed with the various reconstituted particles showed that the binding of proteins L7 and L12 is dependent on the binding of protein L10 and in turn, that the binding of protein L10 is dependent on the binding of protein L11.