  The NF-kB signalling system is involved in a variety of cellular processes
including immune response, inflammation, and apoptosis. Recent experiments have
found oscillations in the nuclear-cytoplasmic translocation of the NF-kB
transcription factor. How the cell uses the oscillations to differentiate input
conditions and send specific signals to downstream genes is an open problem. We
shed light on this issue by examining the small core network driving the
oscillations, which, we show, is designed to produce periodic spikes in nuclear
NF-kB concentration. The oscillations can be used to regulate downstream genes
in a variety of ways. In particular, we show that genes to whose operator sites
NF-kB binds and dissociates fast can respond very sensitively to changes in the
input signal, with effective Hill coefficients in excess of 20.
