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. Together with TatC, TatB is part of a receptor directly interacting with Tat signal peptides. TatB may form an oligomeric binding site that transiently accommodates folded Tat precursor proteins before their translocation. 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; TatB also forms homooligomers. Interacts with the signal sequence of DmsA and DmsD. Localizes at the cell poles. Constitutively expressed. The membrane-extrinsic domain forms parallel contacts with at least one other TatB protein. Disruption blocks the export of seven endogenous Tat substrates. Belongs to the TatB family.