Some readers may have noticed accession codes (A000000) after gene or protein names in some NCB papers (for example, see pages 825 and 837 of this issue). These codes represent unique identifiers that link to a relevant Molecule Page (MP) database entry. This database was set up more than five years ago with the aim of providing a one-stop resource for all relevant and validated information about mammalian signalling molecules. Signalling is defined in a broad sense and currently, the database contains around 4,000 entries. These contain information that is updated frequently from several key databases, such as GenBank, TrEMBL and SwissProt, which provide an overview of gene and protein structure, homologues, motifs and interactions. A growing subset of entries (currently about 10%) contains much more detailed free text information that summarizes the relevant published data for a given signalling molecule. The information is entered by selected experts and subjected to a rigorous peer-review and editorial process. The entries represent authoritative, comprehensive, accessible and citable overviews for a specific signalling component. All information is supported by citations and entries will be regularly updated. The database aims to facilitate systems-level research and therefore the free text information is supplemented by systematic highly structured information that captures all biochemical states and functions of a molecule. These data interlink signalling molecules and allow navigation of the ever more complex signalling web. As such, the MPs are a valuable asset at a time when the concept of linear pathways is breaking down in favour of complex networks that better reflect the reality of most systems.

The interested reader can link directly to the relevant MP using the accession number provided in the text or at the end of the paper. The database is primarily mammalian but contains information on orthologues and we aim to provide links from evolutionarily conserved non-mammalian signalling molecules. The MP database is a free service run by UCSD and NPG, and relies on input from expert authors and referees. Why not apply to contribute — become a molecule biographer and add a high-tech publication to your curriculum vitae! Don't be deterred by the complexity; as Einstein said, 'Things should be made as simple as possible, but not any simpler.'