KEGG is a collection of databases (Figure 1) and connected software tools that integrates genes into pathways linking them functions, diseases, drugs and the like. The KEGG identifiers that are used for the various databases are listed in Figure 2).

KEGG integrates this information via KEGG orthologs (KO) groups across a comprehensive set of species. Yet, KEGG provides an annotation tool BlastKOala (Kanehisa et al. 2016) to propagate information stored in KEGG to sequences from further species. In a nutshell, BlastKOala makes heavy use of phylogenetic relationships among sequences in order to propagate functional annotation of so called KEGG orhtolog groups (KO) to further sequences. It is a Blast based tool that additionally compares domain architectures between the sequences in a KO group and a new candidate.