Chain length determines the folding rates of RNA.

We show that the folding rates (k(F)s) of RNA are determined by N, the number of nucleotides. By assuming that the distribution of free-energy barriers separating the folded and the unfolded states is Gaussian, which follows from central limit theorem arguments and polymer physics concepts, we show that k(F)≈k(0)exp(-αN(0.5)). Remarkably, the theory fits experimental rates spanning over 7 orders of magnitude with k(0)~1.0(μs)(-1). Our finding suggests that the speed limit of RNA folding is ~ 1 μs, [corrected] just as it is in the folding of globular proteins.