We propose a biochemically plausible mechanism for constructing digital logic signals and gates of significant complexity within living cells. These mechanisms rely largely on co-opting existing biochemical machinery and binding proteins found naturally within the cell, replacing difficult protein engineering problems with more straightforward engineering of novel combinations of gene control sequences and gene coding regions. The resulting logic technology, although slow, allows us to engineer the chemical behavior of cells for use as sensors and effectors. One promising use of such technology is the control of fabrication processes at the molecular scale. / DARPA/ONR Ultrascale Computing Program under contract N00014-96-1-1228 and by the DARPA Embedded Computing Program under contract DABT63-95-C130.