A native ribonucleoprotein complex from Escherichia coli ribosomes.

An RNA-protein complex was isolated from the 50S subunit of E. coli ribosomes after trypsin digestion. The complex contains only one protein, L24. Treatment of the complex with pancreatic ribonuclease results in digestion of most of the RNA; however, an RNA fragment of about 100 nucleotides in length is stable to nuclease digestion and remains bound to the protein. It is also possible to reconstitute a complex from 23S RNA and isolated L24; nuclease digestion of this complex produces a resistant RNA fragment of the same size as the native complex. The protein can still bind to 23S RNA after N-methylation of about 20% of its lysine residues. Thus, by use of N-methylated L24 labeled with either (14)C or (3)H, the binding stoichiometry of the reconstituted complex was established; binding of L24 to RNA once again renders the protein trypsin-resistant. This would appear to be a good system for the study of RNA-protein interactions.