Figure 2. RNA helicases and RNA structure remodeling. The majority of RNA helicases are believed to rearrange RNA structure by unwinding dsRNA into ssRNA. Relatively few also catalyze annealing of complementary ssRNA into dsRNA, the annealing and unwinding activities combining to promote RNA strand exchange. These processes require ATP hydrolysis, not for the structure rearrangement but for helicase association with the RNA substrate.^2,127,128 Unwinding generally occurs over short distances, 1–2 helical turns,³ however protein cofactors can increase the processivity and also contribute to RNA substrate specificity.