an L-alpha-D-Hep-(1->5)-[alpha-Kdo-(2->4)]-alpha-Kdo-(2->6)-lipid A + ADP-L-glycero-beta-D-manno-heptose => an L-alpha-D-Hep-(1->3)-L-alpha-D-Hep-(1->5)-[alpha-Kdo-(2->4)]-alpha-Kdo-(2->6)-lipid A + ADP + H(+)