Thermodynamic folding analysis of resolved RNA SIV
leader structures. Shown are predicted free-energy minimized structures from the SIVmac239 wild-type leader (I.) and attenuated mutants pUΔ19 (II.) and pDΔ60 (III.) . Fig. I, arrows labeled a, b, c, and d denote SL1, SL2, SL3 and SL4, respectively, in the SIVmac239 leader structures or their absence in deletion variants.