The present invention relates to novel methods for identifying antiviral agents which selectively interfere with viral proteins that cause the unique infectivity activity of the SARS-coronavirus in comparison to other non-SARS strains of coronavirus. In particular, the present invention relates to screening assays that identify agents which selectively inhibit cyclic-AMP dependent protein kinase activity of the SARS-coronavirus ORF3. The present invention also relates to screening assays that identify agents which selectively inhibit the interaction between SARS-coronavirus cyclic-AMP dependent protein kinase and a calcium dependent targeting molecule. Therefore the agents identified using the assays of the invention may have utility as antiviral agents. The present invention also relates to treatments for sever acute respiratory syndrome caused by a coronavirus, and particularly to treatments that affect the infectivity activity of the SARS-coronavirus. The present invention also relates to diagnostic assays for identifying and characterizing a strain of coronavirus as being one causing severe acute respiratory syndrome.