Phosphotyrosine on STAT2 acts as docking site for STAT1 molecules. STAT1 binds to phosphorylated STAT2 and this is followed by STAT1 phosphorylation on tyrosine residue 701 (Y701). These STATs recruited to the phosporylated IFNAR1 form two distinct transcriptional activator complexes, namely, IFN-alpha-activated factor (AAF) and IFN-stimulated gene factor 3 (ISGF3). AAF is a homodimer of STAT1, whereas ISGF3 is a heterotrimeric complex of STAT1, STAT2 and IRF9 (also known as p48 or ISGF3gamma) (Honda et al. 2005).
SARS-CoV-2 nucleoprotein (N) binds to both STAT1 and STAT2, prevents their phosphorylation, and suppresses their nuclear translocation induced by IFN (Mu J et al. 2020).
Protein tyrosine phosphatases SHP-1 and SHP-2 dephosphorylate JAK1 and STAT1 and suppress their signaling.