STAT1 binds to gp130 via phosphotyrosine residues 905 and 915, these located within two YXPD recognition motifs. STAT3 can also be recruited to these sites as well as two additional sites around Y767 and Y814, these having less restricted sequence recognition requirements (YXXQ) (Gerhartz et al. 1996). Subsequent to receptor binding, these STAT factors are phosphorylated on a single tyrosine residue by JAKs (Hemmann et al. 1996).