  Statistical properties of environments experienced by biological signaling
systems in the real world change, which necessitate adaptive responses to
achieve high fidelity information transmission. One form of such adaptive
response is gain control. Here we argue that a certain simple mechanism of gain
control, understood well in the context of systems neuroscience, also works for
molecular signaling. The mechanism allows to transmit more than one bit (on or
off) of information about the signal independently of the signal variance. It
does not require additional molecular circuitry beyond that already present in
many molecular systems, and, in particular, it does not depend on existence of
feedback loops. The mechanism provides a potential explanation for abundance of
ultrasensitive response curves in biological regulatory networks.
