<p> Proteins in this entry show extensive homology to the ATP synthase F1 beta subunit, and are involved in type III protein secretion. They fall into the two separate functional groups outlined below.</p><p>The first group, exemplified by the <taxon tax_id="602">Salmonella typhimurium</taxon> FliI protein (<db_xref db="SWISSPROT" dbkey="P26465"/>), is needed for flagellar assembly. Most structural components of the bacterial flagellum are translocated through the central channel of the growing flagellar structure by the type III flagellar protein-export apparatus in an ATPase-driven manner, to be assembled at the growing end. FliI is the ATPase that couples ATP hydrolysis to the translocation reaction [<cite idref="PUB00034693"/>, <cite idref="PUB00034694"/>].</p> <p>The second group couples ATP hydrolysis to protein translocation in non-flagellar type III secretion systems. Often these systems are involved in virulence and pathogenicity. YscN (<db_xref db="SWISSPROT" dbkey="P40290"/>) from pathogenic Yersinia species, for example, energises the injection of antihost factors directly into eukaryotic cells, thus overcoming host defences [<cite idref="PUB00034695"/>].</p>