Analysis of total liver RNA for the murine factor IX gene in factor IX-knockout and normal mice by RT-PCR. RT-PCR was performed as described in the Materials and Methods. A 310-bp RT-PCR product was detected in total liver RNA from wild-type but not from the factor IX-knockout mice. RT-PCR products of the factor VII (411 bp) and β-actin (202 bp) genes for the factor IX-knockout mice were no different from those of normal mice. Lanes are as follows: N1 and N2, normal male mice; KO1, KO2, and KO3, factor IX-knockout male mice. The primers used are for the β-actin gene, the murine coagulation factor VII gene, and the murine coagulation factor IX gene as indicated.