We measure a large range of energy pertubations of ∆∆G ‡-U by single point mutations, ranging from ∼ 0 -15 kJ/mol, corresponding to no change in elongation rate up to changes by more than 2 orders of magnitude. We demonstrate that WT seeds elongated with variant monomer can subsequently be elongated with WT monomer and feature the same growth rates within error as fresh WT seeds (Supporting Results). Combined with overall fibril morphology being maintained as evaluated by AFM, we rationalize that the WT fibril structure is propagated throughout our experiments.