Two Specific Ribonucleoprotein Fragments from the 50-S Sub-Particle of Escherichia coli Ribosomes

50-S ribosomal particles from Escherichia coli were hydrolysed with ribonuclease T1, and the ribonucleoprotein fragments produced were fractionated on polyacrylamide gel. The proteins contained in these fragments were analysed on gels containing the detergent sarkosyl (N-laurylsarcosine), using the technique already published. Two-dimensional gel electrophoresis was used for the final identification of the proteins. Two very specific fragments were obtained, the smaller containing only proteins L1 and L9, and the larger containing only L5, L18 and L25. The latter proteins have been shown by other authors to be involved in binding to 5-S RNA, but in this case the fragment contained more RNA than can be accounted for by 5-S RNA alone. This offers the possibility of determining the regions of 23-S RNA associated both with these two groups of proteins and with 5-S RNA. Both fragments are discussed in terms of a possible oligonucleotide analysis of their RNA moieties.