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. Required for PhoD secretion. The cytosolic fraction of TatAd binds the precursor of PhoD. Forms a complex with TatCd. Two types of complexes exist: one composed of TatAd and TatCd, and another composed only of TatAd. Soluble TatAd forms homomultimers bigger than 100 kDa. Soluble TatAd associates in homomultimeric micelle-like particles with a size of about 12 or 25 nm in diameter as well as in elongated particles of 12 nm in diameter. At the onset of phosphate starvation, substantial amounts of TatAd are present in the cytosol. Upon ongoing starvation, the amount of TatAd in the cytosol decreases. Expressed under conditions of phosphate starvation. B.subtilis possesses two minimal, substrate-specific, Tat translocases: TatAd-TatCd and TatAy-TatCy, each one composed of a TatA and a TatC protein. TatA is bifunctional and performs the function of both the TatA and TatB proteins of Gram-negative organisms. Membrane-localization and maintenance of TatAd is assisted by TatCd. Belongs to the TatA/E family.