A new method for the purification of 30S ribosomal proteins from Escherichia coli using nondenaturing conditions

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Abstract
A new method for the purification of E. coli (A19) 30S ribosomal proteins was developed that avoids the use of denaturing conditions such as urea, acetic acid and lyophilization. In this way the majority of the proteins from the small ribosomal subunit can be obtained in 5-100 mg quantities and at .gtoreq. 90% purity. This was achieved by the initial splitting of the proteins into 2 main groups with LiCl followed by fractionating on ion-exchange and gel-filtration columns, in the absence of urea and in the presence of salt. The proteins prepared by this nondenaturing procedure were soluble at high ionic strength and less soluble, being aggregated, at low salt concentrations. This behavior was exactly the opposite of that exhibited by proteins prepared with methods using denaturing conditions. These new methods enabled additional rRNA-binding proteins to be found and potential protein-protein complexes to be isolated. Preliminary evidence that these proteins may retain a more native structure is presented.