Part of the twin-arginine translocation (Tat) system that transports large folded proteins containing a characteristic twin-arginine motif in their signal peptide across membranes. TatA could form the protein-conducting channel of the Tat system. The Tat system comprises two distinct complexes: a TatABC complex, containing multiple copies of TatA, TatB and TatC subunits, and a separate TatA complex, containing only TatA subunits. Substrates initially bind to the TatABC complex, which probably triggers association of the separate TatA complex to form the active translocon. A complex containing only TatA and TatB has also been identified. It could be either an assembly intermediate or a disassembly intermediate generated during translocation activity. Each of TatA, TatB and TatC are able to interact in pairs without the third partner; TatA also forms homooligomers. Abundant all over the membrane, but is more concentrated at the cell poles. Constitutively expressed. TatA is the most highly expressed of the tat genes. Disruption of tatA affects the correct localization of multiple enzymes whose precursors bear twin arginine transfer peptides. Export is completely blocked when both tatA and tatE are inactivated. TatA forms a transmembrane channel with a lid structure on the cytoplasmic side. The number of TatA protomers can vary so that the channel can adopt different diameters to accommodate substrates of various sizes. This enables TatA to pack tightly around substrate and prevents ion leakage during transport. Absence of TatA from the TatBC complex leads to the instability of the complex and the specific breakdown of TatB. Belongs to the TatA/E family. Extended N-terminus.