  Developing and maintaining life requires a lot of computation. This is done
by gene regulatory networks. But we have little understanding of how this
computation is organized. I show that there is a direct correspondence between
the structural and functional building blocks of regulatory networks, which I
call regulatory motifs. I derive a simple bound on the range of function that
these motifs can perform, in terms of the local network structure. I prove that
this range is a small fraction of all possible functions, which severely
constrains global network behavior. Part of this restriction is due to
redundancy in the function that regulatory motifs can achieve - there are many
ways to perform the same task. Regulatory motifs help us understanding how
genetic computation is organized and what it can achieve.
