Effects of detergents on the conformation of Escherichia coli tRNA as measured by circular dichroism.

The effect of a cationic detergent, lauryl pyridiniumchloride (LPC), and an anionic one, sodium n-octylbenzenesulfonate (SOBS), on the conformation of unfractionated Escherichia coli tRNA was investigated at various molar ratios of detergent to tRNA (D/R) in the presence and absence of Mg2+ and Na+ ions by measuring the circular dichroism (CD) at 265 nm and 340 nm, which reflects conformational change involving base pairs and/or base stacking, and the disymmetry in the vicinity of 4-thiouridylate (4-TU), respectively. In the presence of Mg2+ and Na+ ions, the tRNA retains its native structure even in the presence of high molar ratios of detergent to tRNA (D/R congruent to 40 at 265 nm and D/R congruent to 20 at 340 nm). However, in the absence of these metal ions, the ellipticity at 340 nm was very sensitive to LPC concentration and decreased from 5,600 to nearly--1,600 at 25 degrees C with the increase of D/R ratios up to 20, and a similar decrease in the ellipticity at 340 nm was observed on thermal denaturation. This result suggests that the local environment involving the 4-TU region might be readily influenced by LPC, reflecting a large conformational change. However, no effect was observed in the case of the SOBS: tRNA system. On the other hand, secondary base pairing and/or base stacking structure was virtually invariant on adding both LPC and SOBS even at high D/R ratios in the absence of Mg2+ and Na+ ions.