to summarize the content of EcoCyc, to assess its completeness, and to deﬁne areas for further research. Examples include the list of regulatory signals in Table 4, and the list of unsequenced E. coli enzymes at http:// ecocyc.org/enzymes.shtml. Other programs assess the biological coherence of the data in EcoCyc, such as by propagating nutrients from known growth media through the EcoCyc metabolic network to assess whether the network can produce compounds essential for growth from a known minimal medium, and by searching for dead-end metabolites. ACKNOWLEDGEMENTS This work was supported by grants GM077678, GM075742 and GM071962 from the National Institutes of Health. The contents of this publication are solely the responsibility of the authors and do not necessarily represent the oﬃcial views of the National Institutes of Health. We are grateful to Dr Robert Gunsalus for comments on this manuscript, and for his many sugges- tions regarding EcoCyc. 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