Additionally, the S protein containing S1 and S2 domains can be cleaved by Furin or transmembrane serine protease 2 (TMPRSS2) to accelerate the virus-cell membrane fusion and increase the viral tropism to organs, which may justify why SARS-CoV-2 has a higher infection rate than SARS-CoV. The gene discussed is TMPRSS2; the disease is infection.