The Tat protein export pathway

The Tat (twin-arginine translocation) system is a bacterial protein export pathway with the remarkable ability to transport folded proteins across the cytoplasmic membrane. Preproteins are directed to the Tat pathway by signa l peptides that bear a characteristic sequence motif, which includes consec utive arginine residues. Here, we review recent progress on the characteriz ation of the Tat system and critically discuss the structure and operation of this major new bacterial protein export pathway.