Hypothesis: the RNase-sensitive restraint to unfolding of spermidine nucleoids from Escherichia coli is composed of cotranslational insertion linkages Original Research Article

The genomic DNA of bacteria is highly localized in one or a few bodies known as nucleoids. A number of restraints to the unfolding of the DNA of spermidine nucleoids from Escherichia coli were previously associated with characteristic urea concentrations (Um values). The dominant restraint to unfolding was sensitive to pancreatic RNase and underwent a cooperative transition at Um=3.2 M urea. The losses of the RNase-sensitive restraint caused by urea or pancreatic RNase appear to result from breakage of cotranslational insertion linkages which joined the nucleoid to the cell envelope in growing cells. This conclusion is based upon effects from exposures of cells to antibiotics (chloramphenicol, rifampicin, streptomycin), treatment of nucleoid preparations with formaldehyde or concentrated NaCl solutions, and effects of urea on purified ribosomes. The specific RNase-sensitive and urea-sensitive components of the spermidine nucleoids are suggested to be the mRNA and ribosomes, respectively, of cotranslational insertion linkages.