Phosphorylated Jak1 (p-Y-Jak1) phosphorylates the Stat proteins Stat1 (de Koning et al. 1996, Nicholson et al. 1996, Shimoda et al. 1997), Stat3 (Nicholson et al. 1995, de Koning et al. 1996, Nicholson et al. 1996, Shimoda et al. 1997, Chakraborty et al. 1999, de Koning et al. 2000), and Stat5 (de Koning et al. 1996, Nicholson et al. 1996, Shimoda et al. 1997, Dong et al. 1998, Ward et al. 1999, Gits et al. 2006) at the cytosolic domain of Csf3r (G-CSFR). Phosphorylated Jak2 acts redundantly with p-Y-Jak1 to phosphorylate Stat proteins (Gits et al. 2006).