Interaction between Membrane Functions and Protein Synthesis in Reticulocytes: Specific Cleavage of 28‐S Ribosomal RNA by a Membrane Constituent

A factor isolated from rabbit reticulocyte white ghosts by Triton X‐100 treatment blocks protein synthesis at the elongation‐termination stage. Factor‐treated ribosomes were found to have an identical buoyant density to that of control ribosomes. When incubated with either reticulocyte ribosomes or ribosomal RNA, the factor products specific cuts in the 28‐S ribosomal RNA component without damaging the 18‐S RNA. Incubations of pancreatic or T₁ RNase, with ribosomal RNA, at similar protein‐synthesis inhibitory concentrations effected a complete breakdown to oligo and mononucleotides. When challenged with isolated 28‐S or 18‐S reticulocyte ribosomal RNA, the highly purified factor only attacked the 28‐S RNA species. There was no accumulation of nucleotides or oligonucleotides and we concluded that the membrane factor causes inhibition of protein synthesis by having a specific endonucleolytic cleavage activity.