7586 Nucleic Acids Research, 2007, Vol. 35, No. 22 Figure 6. Representative region of the E. coli genome generated by the EcoCyc genome browser. UC Santa Cruz Genome Browser (24). Figure 7 shows the use of tracks to display predicted promoters in a region of the E. coli genome. Comparative views of several genomes for organisms within the BioCyc collection of 370 organism-speciﬁc PGDBs can easily be generated from within a BioCyc gene page from any organism by clicking on the button ‘Align in Multi-Genome Browser’ mid-way down the gene page, and then selecting the organisms for which a comparison is desired. The resulting visualization, such as that shown in Figure 8, aligns the genomes at the orthologs to the starting gene in the selected organisms, and displays the adjacent chromosomal regions to scale. The same naviga- tion panel used in the regular genome browser can be used to scale and position the comparative genome browser. In the comparative genome browser, colour no longer encodes operon membership: genes drawn in the same colur are orthologs of one another (best bi-directional BLAST hits). Tens of other E. coli strains have been sequenced to date, and additional E. coli strains are being added to the BioCyc collection on an ongoing basis. We note that the K-12 strain described by EcoCyc is smaller, by more than 1000 genes, than other sequenced E. coli strains.