Signal transducer and activator of transcription 1-alpha/beta (STAT1), STAT3, STAT5A and STAT5B bind to the Interleukin-9:Interleukin-9 receptor (IL9:IL9R). Mutation of IL9R phosphorylated tyrosine-116 abolished activation of STAT1, STAT3 and STAT5 (Demoulin et al. 1996, Bauer et al. 1998). Other residues near this position are involved in determining which STAT binds to the receptor (Demoulin et al. 1999).