STAT1 binds to IL6ST (gp130) via phosphotyrosine residues 905 and 915 within two YXPD recognition motifs. STAT3 can be recruited to these sites and to two additional sites around Y767 and Y814 that have less restricted sequence recognition requirements (YXXQ) (Gerhartz et al. 1996). After receptor binding, STATs are phosphorylated on a single tyrosine residue by JAKs (Hemmann et al. 1996).