Figure 7.

Model for the dimerization of the TAR/1 complex. The TAR-RNA with one molecule of 1 bound to the upper stem major groove dimerizes through an aminoglycoside molecule bound to the lower stem minor groove. The two RNA molecules are oriented with the lower stems roughly parallel to each other (interhelical angle θ ≈ 30°) and the upper stems diverging from each other. From the magnetic susceptibility tensor of the dimeric RNA a dipolar coupling tensor can be calculated (D_zz, 6.8 Hz; R, 0.54), which fits well the experimentally determined one (36). The color-coding is the same as in Figure 5.