This phenotypic error threshold suggested two important considerations: known ribozymes by the virtue of their small sizes could be replicated by replicases whose accuracy would not have surpassed those of experimentally produced, available polymerase ribozymes, and a replicase working at an error rate one magnitude lower than the currently known polymerase ribozymes could have replicated a small genome of a complete ribo-organims. In this paper, we broaden the investigation of the error threshold into important directions. What structural characteristic of RNAs determines the position of the phenotypic error threshold? More specifically, can the degree of neutrality be employed to LY2109761 estimate the error threshold as proposed in. Please note, that the formula in Eq. 2 was derived by assuming that the effect of mutations are independent, and thus if there is two mutations that are independently neutral, then a sequence having both of them together will still be neutral. This is not necessary true. Furthermore the degree of neutrality is assumed to be the same for every sequences of the master type. We know that there places of different degree of neutrality along neutral paths. Moreover, note that this formula is obtained at zero concentration of the master phenotype, which condition cannot occur when there is back mutation, especially in case of short sequences; it therefore gives an overestimate of the error threshold. In our analysis we start from Eigen’s quasispecies model and based on fitness landscapes of folded RNA we analytically calculate the error threshold, and correlate it with structural characteristic, thereby checking Eq. 2. How general is our previous finding that even lowaccuracy replicases could replicate the known ribozymes if only the former were processive enough ? Note that the best experimentally verified polymerase ribozyme, while being 198 nt long, can copy sequences up to 95 nt or can copy a very specific template up to 206 nt. If Eq. 2 can be used to estimate the error threshold, then we can make a rough estimate for known ribozyme sequences from the literature, and strengthen our previous claim. We consider the above raised questions in turn. Finally, we look at the world of putative ribo-organisms in the light of our findings. The position of the error threshold for an arbitrary fitness landscape and in the presence of back mutations is a matter of definition in the quasispecies model of Eigen. We have calculated the error threshold for binary sequences up to length 16. Sequences comprising of only GC nucleotides have similar structural diversity as those composed of all four bases, and thus our results are representative for them as well.