A group lead by Luc Jaeger at UCSB is reporting  in the Dec. 17 2004 issue of Science that they now can program RNA building blocks to self-assemble into complex shapes. Interestingly if extended slightly and combined with certain chemical mixthres that polymerize or perhaps light-hardened polymers one could use the RNA pieces to create casting molds that would allow you to "cast" nanoscale parts with relatively precise atomic dimensions and a relatively high density of covalent bonds. More…
1. Chworos A, Severcan I, Koyfman AY, Weinkam P, Oroudjev E, Hansma HG, Jaeger L., "Building programmable jigsaw puzzles with RNA," Science 306(5704):2068-72 (17 Dec 2004).
Interestingly, Nadrian Seeman has a report in the same issue of Science for a "nanomechanical DNA device" which from the abstract appears to be a DNA state machine [Is this a prelude to a DNA based Turing machine assembler???]. As currently designed it is driven by DNA and produces DNA but it does not appear to use the normal base pair "matching" which is required by DNA polymerase (which is also effectively a DNA assembler). However because it is a DNA based assembler that produces DNA that would suggest that the potential for exponential growth in the quantity of devices available is very high. (Mind you the potential may not be there yet — one has to deal with things like transport time for the instructions and error correction of the product — but the potential seems to be there).
2. Liao S, Seeman NC., "Translation of DNA signals into polymer assembly instructions," Science 306(5704):2072-4 (17 Dec 2004).