Fractionation of transfer ribonucleic acids by chromatography on neutral polysaccharide media in reverse salt gradients

High-performance liquid chromatography of tRNAs on novel stationary phases

Rapid separation of a group of tRNAs was carried out on novel siliceous bonded stationary phases with aqueous eluents by using gradient elution with increasing or decreasing salt gradient, as usual in electrostatic interaction chromatography or hydrophobic interaction chromatography, respectively. The stationary phases consist of microparticulate macroporous silica with surface-bound polar moieties, containing weak cationic and/or hydrophobic binding sites. Depending on the nature of the binding sites, the stationary phases exhibit different retention behavior and selectivity for tRNAs. Aqueous phosphate solutions were used as the eluent, and in many cases isocratic elution was sufficient to separate seven tRNAs. Addition of magnesium ions or n-decylbetaine to the eluent resulted in lower retention, the latter causing a greater increase in the eluent strength. The optimum pH range of the eluent was 5.5-6.5.

Reverse salt gradient chromatography of tRNA on unsubstituted agarose. I. Variations in elution profile and evidence for two fractionation mechanisms

E. coli tRNA was fractionated by the application of ammonium sulphate reverse gradients to Sepharose 4B. Variations in elution profile were partly attributable to differences between batches of Sepharose. The profile also varied with column length and gradient parameters. This suggests the existence of two distinct mechanisms which do not separate different tRNAs in the same sequence. The first mechanisms, believed to be interfacial precipitation, releases tRNAs progressively as the salt concentration is reduced. A second mechanism introduces adsorptive retardation in which molecules lag behind the solvent. This process, widely believed not to be important in the chromatography of macromolecules with multiple binding sites, is in the present case mainly responsible for the improved resolution of peaks on passage down a long column. Isocratic (constant-salt) fractionation is also feasible. The Sepharose batch variation affects the second mechanism more than the first.

Reverse salt gradient chromatography of tRNA on unsubstituted agarose. II. Further study of binding mechanisms

The existence of two mechanisms in the fractionation of tRNA on Sepharose 4B, using reverse gradients of ammonium sulphate, was confirmed by comparing yeast and E. coli tRNAs, and by extending the range of conditions used. The difference in elution range between the two kinds of tRNA is attributable mainly to variations in tight binding rather than adsorptive retardation. Variations of pH or of temperature produce not only changes in peak distribution, but overall shifts in the elution profile. The shifts correlate closely with changes in the solubility of tRNA in free solution, confirming that tight binding is associated with interfacial precipitation. On the other hand the degree of adsorptive retardation, as indicated by the difference between elution profiles from long and short columns, is quite similar under all conditions. It is if anything slightly greater at 25 degrees C than at 5 degrees C, implying a binding mechanism analogous to hydrophobic bonding. Binding-equilibrium studies suggest that the effect is related to the formation of a monolayer of tRNA on the agarose threads of matrix. Experiments with hydroxyapatite also demonstrate adsorptive retardation, comparable in degree to that observed with Sepharose. This indicates that the effect may be much more important in ion-exchange chromatography than is normally assumed.

Preparative scale fractionation of Escherichai coli robosomal RNA and transfer RNA on Sjepharose 6B

Total Escherichia coli RNA has been fractionated on Sepharose 6B in 0.1 M ammonium acetate, pH 5.0. The elution order was 23S rRNA, 16S rRNA,, 5S rRNA, and tRNA, which is in contrast with the reported elution order of eukaryotic RNA, chromatographed under similar conditions. tRNA was obtained in two regions, well separated from the high molecular weight rRNA but with a slight contamination of 5S rRNA. The capacity is at least 40 A260 units of RNA per ml of gel.