By designing four primers for an overlapping PCR, we created a fusion gene Ddlcat encoding human TNF receptor I death domain and chloramphenicol acetyltransferase (CAT). By DNA sequencing, the whole sequence of the fusion gene is confirmed to be correct. Two hours after induction with IPTG, we could see a 39 kD extra protein band on SDS-PAGE pattern. We proved that this 39 kD protein band is DdLcat protein by Western blotting. Then we purified this protein to the purity of 95% through Q-Sepharose chromatography.