Catalytic subunit of the tagatose-1,6-bisphosphate aldolase GatYZ, which catalyzes the reversible aldol condensation of dihydroxyacetone phosphate (DHAP or glycerone-phosphate) with glyceraldehyde 3-phosphate (G3P) to produce tagatose 1,6-bisphosphate (TBP). Requires GatZ subunit for full activity and stability. Is involved in the catabolism of galactitol. D-tagatofuranose 1,6-bisphosphate = D-glyceraldehyde 3-phosphate + dihydroxyacetone phosphate Binds 1 zinc ion per subunit. Carbohydrate metabolism; D-tagatose 6-phosphate degradation; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-tagatose 6-phosphate: step 2/2. Forms a complex with GatZ. Belongs to the class II fructose-bisphosphate aldolase family. TagBP aldolase GatY subfamily.