A ribonucleoprotein core in the 50 S ribosomal subunit of Escherichia coli

Many methods have been used for investigating the structural organisation of the ribosome. Although steady progress has been made in characterising both the RNA and protein regions that are accessible on the surface of the ribosome and the approximate locations of the RNA binding sites of the proteins, little is known about the internal organisation of proteins and RNA in the ribosomal subunits (reviewed in PI>. Recently, evidence has accumulated for the presence of a large RNA core in the 5’+ne third of 23 S RNA; when protein L24 is bound, based on: (i) Limited ribonuclease digestion [2]. (ii) Electron microscopy [3]. (iii) Physical chemical studies [4], (iv) Identification of RNA-RNA interactions between widely separated sequence regions [5 ] in a complex of protein L24 and 23 S RNA. There are also indications that a stable proteinRNA core may exist in 50 S subunits which includes this RNA region and a small group of proteins. The evidence derives from three main sources: (i) In vitro assembly of 50 S subunit proteins to large fragments of 23 S RNA [6]. (ii) Intermediate particles formed during in vitro assembly of 50 S subunits [7]. (iii) Studies on protein-depleted ribosomes prepared in high salt [8-l0