Conclusion of Progress Report  

This concludes our description of the major results obtained so far in our ongoing research project to demonstrate the significant computational power of systems of DNA molecules. In the work presented above, we have invented a new method for using oligo-directed mutagenesis using mixtures of oligos to perform a programmed series of mutations in subsequent generations of descendants of an initial template piece of DNA. We have demonstrated via detailed computer simulations that the power of this technique is sufficient to allow strands to approximately count the number of generations of copying that separate them from the original template, and to allow the execution of simple Turing machines. We have demonstrated that the technique we use for implementing simple Turing machines could also be applied in a straightforward way to implement arbitrarily complex Turing machines, including ones that are computation-universal and nondeterministic. Results of computations can be straightfowardly extracted. Since the computational mechanism requires absolutely no external intervention other than the signal to begin replication, it is also conceivable, although still somewhat speculative, that something similar to the process described here might be able to work within living cells, in which case there could be significant practical applications in medicine. Moreover, if cells do this sort of string-rewriting already, it could explain some aspects of the development and differentiation of cell lines. Finally, the technique presents opportunities for practical applications in vitro, such as creating scalable molecular computers for solving extremely large and difficult computational search problems requiring astronomically high degrees of parallelism. The world is about to enter the age of molecular computing.