Catalyzes the reversible formation of fructose 6-phosphate from dihydroxyacetone and D-glyceraldehyde 3-phosphate via an aldolization reaction. beta-D-fructose 6-phosphate = D-glyceraldehyde 3-phosphate + dihydroxyacetone Homodecamer. Belongs to the transaldolase family. Type 3A subfamily.