How is STAT5 recruited and activated in the JAK-STAT pathway?

STAT5 is activated by receptor dimerization.

STAT5 is recruited by binding to phosphorylated tyrosine residues on the cytokine receptor and activated by JAK2 phosphorylation.

STAT5 is recruited by binding to unphosphorylated cytokine receptors.

STAT5 is directly phosphorylated by the ligand.