SUMMARY: The unusual particles which accumulate in cell-free extracts from A19 during chloramphenicol inhibition (‘chloramphenicol particles’) have been isolated by large-scale rate-zonal density gradient ultracentrifugation. The proteins and RNA species composing these particles have been examined.

The rRNA species present are precursor and mature forms of 16S and 23S rRNA which accumulate during inhibition. The proteins prepared directly from the particles give strong multiple immunoprecipitates with antisera specific to 30S and 50S ribosomal proteins. The soluble proteins of the cell prepared in the same manner do not give this immunological reaction. Two-dimensional electrophoresis patterns of the proteins from the ‘chloramphenicol particles’ strongly resemble those for 30S and 50S ribosomal proteins, i.e. they are predominantly basic low molecular weight proteins, and are dissimilar to the patterns for the soluble proteins of the cell.

It is concluded that the ‘chloramphenicol particles’ are a heterogeneous group of ribonucleoproteins comprising the bulk of the rRNA accumulating during inhibition in association with variable amounts of some of their corresponding ribosomal proteins. The particles are therefore not artefacts of preparation, as previously thought, but arrested ribosome precursors.


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