Biomolecular implementation of computing devices with unbounded memory

We propose a new way to implement (general) computing devices with unbounded memory. In particular, we show a procedure to implement automata with unbounded stack memory, push-down automata, using circular DNA molecules and a class IIs restriction enzyme. The proposed ideas are inspired by the results from [1]. The same ideas are extended to show a way to implement push-down automata with two stacks (i.e, universal computing devices) using two circular molecules glued with a DX molecule and a class IIs restriction enzyme. In this case each computational molecule also contains a DX portion. These devices can potentially be incorporated in an array of TX molecules.