Lysates were prepared from the indicated human CML K562 cell line (Lane1), a patient with chronic myelogenous leukemia (lane 2), and 5 patients with chronic MPNs (Lanes 3–7). Patient 1: non-CML CMPD, JAK2 V617F positive; Patient 2: non-CML CMPD, JAK2 V617F negative; Patient 3: non-CML CMPD, JAK2 Δexon14 positive; Patient 4: non-CML CMPD, JAK2 Δexon14 positive; Patient 5: non-CML CMPD, JAK2 Δexon14 positive. Top Panel: Probing with an anti-JAK2 N-terminal clone yielded a wild-type JAK2 band at 130 kDa in the K562 and other negative control lanes, and an additional band at 75 kDa only in patients with expression of Δexon14 transcript. Bottom Panel: An anti-JAK2 clone directed against the carboxyl-terminus of JAK2 yielded only a single band at 130 kDa.