Dominant negative JNK1 (Mapk8) and JNK2 (Mapk9) cDNAs in which the dual phosphorylation motif TPY was changed to APF were each fused to a 5.5 kb cardiac specific alpha myosin heavy chain promoter. The constructs were mixed and coinjected into FVB/N oocytes. Three independent lines including 22.4 which was chosen as a representative, and 6.1 were found to coexpress equal amounts of each dominant negative protein.