A large nucleoprotein fragment of the 50-S ribosomal subunit of Escherichia coli.

A large nucleoprotein fragment was isolated from a nuclease digest of Escherichia coli 50-S ribosomes and purified to gel electrophoretic homogeneity. Conditions were employed under which the fragmentation pattern was reproducible and the various fragment fractions were stable and maintained their sedimentation and electrophoretic properties throughout the several preparative and analytical procedures used. Fractions that appeared homogeneous in sucrose gradient centrifugation were found to be heterogeneous by gel electrophoresis. The large fragment was purified to homogeneity by preparative gel electrophoresis. It contained 21 proteins, the 5-S RNA, and two large oligonucleotides which together total about two thirds the molecular weight of the 23-S RNA. Because it can be prepared reproducibly in large quantities and because of its size and stability, the fragment appears suitable for functional and structural studies and as the starting material for further fractionation. An important contributing factor to the observed stability and reproducibility was the maintenance of an unchanging ionic environment. A single buffer was employed throughout all the procedures, and the fragments produced by nuclease digestion were dissociated from each other by heat rather than by changing the medium.