You should read some of the genetic computing papers (I think the one on computing paths on a graph was posted here the other week.). My understanding is that

You should read some of the genetic computing papers (I think the one on computing paths on a graph was posted here the other week.). My understanding is that DNA oligimers can interact with each other directly and perform what are essentially string operations. Like most systems that can perform string operations on themselves this appears to be capable of universal computation.