In TGEV-infected cells, nsp1 is distributed in both the nucleus and the cytoplasm, which is not surprising as it can freely diffuse into the nucleus because of its small molecular weight (∼9 kDa). In contrast to TGEV nsp1, both MHV nsp1 and SARS-CoV nsp1 are localized exclusively in the cytoplasm of virus-infected cells. Due to its binding to the 40S ribosomal subunit, nsp1 inhibits cellular mRNA translation in some cases (HCoV-229E and HCoV-NL63) but not in others (TGEV). In addition, nsp1 inhibits IFN induction and signaling.