No abstract

When Escherichia coli 30‐S ribosomes are treated with 6 M urea in the presence of Mg2+, their sedimentation coefficient drops to 16–17 S, and their circular dichroism spectrum changes in a way that indicates a change in the conformation of the proteins in the ribosome. Under these conditions proteins are detached by relatively low concentrations of salt, NH4Cl and magnesium acetate being comparably effective. The proteins remaining attached to the RNA at different ionic strengths have been identified. It is concluded that the conformation of the proteins in situ in the ribosome is a determining factor affecting the structure of the ribosome and the detachment of the proteins by salt.

No abstract

A stable homogeneous ribonucleoprotein fragment of the 30 S ribosomal subunit of E. coli has been prepared by mild nuclease digestion and heating in a constant ionic environment. The fragment contains about half of the 16 S ribosomal RNA and six proteins: S4, S7, S9, S13, S16 and S19. The RNA moiety contains the reported binding sites of all six proteins. After deproteinization, 80% of the RNA migrated as two major electrophoretic bands, which were isolated and sequenced. Each band contained sequences from the 5' and 3' thirds of the 16 S RNA but none from the central third. That these two noncontiguous RNA domains migrated together electrophoretically in Mg++-containing gels after deproteinization constitutes direct evidence that the 16 S RNA is folded in the intact ribosome so as to bring the two domains close together and that there are RNA-RNA interactions between them in the presence of Mg++.

No abstract