A ribonucleoprotein component of Escherichia coli

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Abstract
The analytical ultracentrifuge was used to study certain particles in cell-free extracts of E. coli. The main ribonucleoprotein component sedimented at 40 Svedberg units (un-corrected). Its concentration was greater in cells grown with peptone than with mineral-salts media containing the same concentration of glucose. The component disappeared when cells were incubated at 37[degree]C with 0.13[image]-phosphate buffer, pH 7; this was prevented by addition of 1.6 m[image]-magnesium sulphate. When the phosphate concentration was reduced, the disappearance was slower and was not observed in 0.03 [image]-phosphate buffer in the absence of magnesium ions. Cells were also depleted of the component when incubated with 0.31 [image]-potassium chloride. When "depleted" cells were incubated with magnesium sulphate the component was re-formed within 20 minutes. At high magnesium sulphate concentrations, depending on the density of the cell suspension, a sharp boundary in schlienen diagrams showed that an apparently homogeneous component was reformed; but at lower Mg concentrations there was an additional boundary of slightly lower sedimentation coefficient. This heterogeneity was also evident in extracts from cultures grown to high populations and from peptone-grown cells after "depletion." "Depleted" cells synthesized [beta]-galactosidase at the same rate as cells containing higher concentration of the "40s component." Isolated "40s component" was stable in 0.31 [image]-potassium chloride. In 0.13 [image]-phosphate buffer, material that sedimented mainly at 27 and 17 Svedberg units was formed; in 0.05 [image]-sodium citrate all products of disintegration sedimented slower than 11 Svedberg units. Ribonucleic acid still migrated with protein during electrophoresis of material after disintegration. From a consideration of the extracellular concentrations of salts which produce the observed reversible changes within cells it is concluded that ribonucleoprotein components sedimenting faster than 40 Svedberg units are not indispensable for normal cell metabolism.