Table 1.

Summary of notation used in this article

CVtot	Total noise in protein numbers.
CVext	Extrinsic noise in protein numbers.
CVint	Intrinsic noise in protein numbers.
CVz	Noise in the exogenous signal driving the gene network.
CVtot–nr	Total noise in protein numbers when there is no feedback.
CVext–nr	Extrinsic noise in protein numbers when there is no feedback.
CVint–nr	Intrinsic noise in protein numbers when there is no feedback.
CVtot–min	Minimum possible total noise in protein numbers with optimal negative feedback.
CVext–min	Minimum possible extrinsic noise in protein numbers with optimal negative feedback.
CVint–min	Minimum possible intrinsic noise in protein numbers with optimal negative feedback.
amin	Feedback strength where the total noise in the protein is minimum.
x∗	Steady-state mean protein level.
Tr	Protein response time.
Tnr	Protein's half-life.
Tz	Response time of the exogenous signal.