yscN is the first gene of the virB locus on pYV and encodes a 47.8-kDa protein similar to the catalytic subunits of F0F1 and related ATPases, with Walker boxes A and B. A box A deletion mutant is impaired in Yop secretion and is complemented in trans by cloned yscN.

The protonophore CCCP inhibits Yop secretion as well as motility, showing that Ysc type III secretion requires the proton motive force; MotA/MotB are not involved.

The Salmonella SPI-1 ATPase InvC recognizes substrates and induces chaperone release and substrate unfolding in an ATP-dependent manner.

Purified His-YscN is a cooperative ATPase; His-YscL inhibits it non-competitively. YscN and YscL interact in the cytoplasm of Y. enterocolitica, and GST-YscL copurifies YscN and YscQ.

Impassable YopR hybrids capture YscN in the bacterial cytoplasm and block type III secretion; the first eleven residues of YopR constitute the secretion signal required for YscN binding. Purified His-YscN binds YopR-GST but not GST-YopR or signal-deleted YopR.

EGFP-YscN assembly requires YscC, YscJ, YscK, YscL and YscQ. YscN forms a hexameric ring at the cytosolic side of the injectisome. Secretion is complemented by wild-type yscN but not by the Walker-box mutant K175E, which nevertheless still supports C-ring formation, showing that the ATPase requirement for sorting-platform assembly is structural.

SctN/YscN is one of five conserved cytosolic components, thought to detach chaperones and unfold export substrates; SctO/YscO is homologous to the central stalk of the FoF1-ATPase and stimulates its ATPase activity. In the absence of YscQ-C, EGFP-YscN remains completely cytosolic.

YscN is an oligomerization-activated ATPase and a peripheral member of stable cytosolic YscK/YscQ/YscL/YscN complexes; deletion of yscN strongly destabilizes those complexes.

The homologous flagellar export ATPase FliI is a Mg2+-dependent ATPase whose activity is unaffected by F-, V- and P-type ATPase inhibitors.

In the homologous flagellar export system the membrane export gate itself is the proton-protein antiporter; the soluble ATPase does not conduct protons.

FlhA, a membrane component of the flagellar export gate, has ion channel activity, and its interaction with FliJ allows effective use of the PMF for protein export.

Identifies P40290 as the Ysc-Yop injectisome ATPase and explicitly warns that YsaN, the ATPase of the chromosomal Ysa-Ysp T3SS of the same organism, is a different protein whose biochemistry must not be transferred to P40290.