Why is the phosphorylation and dimerization of STAT5 significant in the JAK-STAT pathway?

• A. It prevents the recruitment of JAK Tyrosine Kinase.
• B. It inhibits the JAK-STAT signaling pathway.
• C. It causes the cytokine receptor to degrade.
• D. It allows STAT5 to function as a transcription factor, regulating gene expression in the nucleus.

Answer: (D)