Protein-lysine methyltransferase that selectively trimethylates citrate synthase (CS) in mitochondria. Seems to conduct trimethylation in a highly distributive manner rather than in a processive manner, and thus introduces a single methyl group per binding event. L-lysyl-[citrate synthase] + S-adenosyl-L-methionine = H(+) + N(6)-methyl-L-lysyl-[citrate synthase] + S-adenosyl-L-homocysteine N(6)-methyl-L-lysyl-[citrate synthase] + S-adenosyl-L-methionine = H(+) + N(6),N(6)-dimethyl-L-lysyl-[citrate synthase] + S-adenosyl-L-homocysteine N(6),N(6)-dimethyl-L-lysyl-[citrate synthase] + S-adenosyl-L-methionine = H(+) + N(6),N(6),N(6)-trimethyl-L-lysyl-[citrate synthase] + S-adenosyl-L-homocysteine Citrate synthase-lysine methyltransferase activity is inhibited by S-adenosylhomocysteine (AdoHcy) and oxaloacetate (OAA). Belongs to the methyltransferase superfamily.