Three architectures and
two modes for the molecular control of
transcription manifested by two-gene circuits with an extra first-order
process involved in the maturation of the functional form for each
regulator. Architectures: (a) Negative feedback loop, (b) positive
and negative feedback loops, and (c) positive and nested negative
feedback loops. Combinations of two modes of molecular control: (d)
activator-primary and (e) repressor-primary. The symbols are the following:
NA, nucleic acid precursors; mRNA, messenger RNA; A, activator; R,
repressor.