Control by bacteriophage T4 of two sequential phosphorylations of the alpha subunit of Escherichia coli RNA polymerase

The effect of 2′-O-methylation upon the base-stacking properties of dinucleoside monophosphates has been studied by circular dichroism measurements over the temperature range from ?20 °C to +80 °C at high and at low salt concentration of 13 2′-O-methyl derivatives in neutral aqueous solution. It is found that 2′-O methylation generally enhances the stacking propensity of dinucleoside monophosphates except for the dimers with adenine in the 3′-linked nucleoside, where the converse trend is observed. The influence of 2′-O-methylation upon the base-stacking property of a dimer correlates in part with the effect of a reduction in salt concentration, suggesting that the 2′-O-methyl group effects the stacking by displacing ions from the immediate environment of the dimer as well as by intramolecular steric effects. The dimers which exhibit an enhanced stacking due to the 2′-O-methylation are found in a larger than statistical abundance in yeast transfer RNA, whereas those showing a reduced stacking occur in minor abundance. These observations are discussed in relation to some current views on the role of modified nucleosides in the conformation of ribonucleic acids.