Rhomboid serine protease that catalyzes intramembrane proteolysis. Mediates quorum-sensing and the subsequent regulation of target genes via activation of the Tat protein export system. Catalyzes the proteolytic activation of TatA by removal of its N-terminal extension. Cleaves type-1 transmembrane domains using a catalytic dyad composed of serine and histidine that are contributed by different transmembrane domains. AarA deletion mutations display alterations in cell morphology and total or partial loss of yellow pigmentation. Belongs to the peptidase S54 family.