Ankyrin repeats are one of the most abundant repeat motifs, and generally function as scaffolds for protein-protein interactions in processes including cell cycle, transcriptional regulation, signal transduction, vesicular trafficking, and inflammatory response. Although predominantly found in eukaryotic proteins, they are also found in some bacterial and viral proteins. Less is known of their physiological roles in prokaryotes. Some bacterial ANK proteins play key roles in microbial pathogenesis by mimicking or manipulating host function(s). The pathogen Providencia alcalifaciens N-formyltransferase ankyrin repeats function in small molecule binding and allosteric control. Ankyrin-repeat proteins have been associated with a number of human diseases.