Leader protein (nsp1) begins restructuring the host cell after infection and is highly divergent between corona viruses.
It binds to the ribosome (40S subunit) and slows down the infected cell’s own protein production, while enabling production of viral proteins. This helps prevent the cell aiding an immune response and forces it help the virus proliferate.
Nsp1 also induces host mRNA cleavage (but is not a nuclease itself) and a variety of chemical changes in the host cell, which are not yet fully understood.