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. Required for PhoD secretion. TatCd promotes membrane localization of TatAd via domain specific interactions. TatCd is required for stabile production of TatAd as well as for its maintenance. Forms a complex with TatAd. Two types of complexes exist: one composed of TatAd and TatCd, and another composed only of TatAd. Expressed under conditions of phosphate starvation. Depletion of TatCd results in a drastic reduction of TatAd. 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. Belongs to the TatC family.