Effect of JAK2V617F on Lu phosphorylation in BaF3 and HEL cells. Quantification of Lu, Lu(v13), and LuS621A phosphorylation in (A) BaF3 and (B) HEL cell lines in the presence or absence of JAK2 inhibitors HBCH or Z3. The top (P) and bottom (WB) panels show the phosphorylation and the total amount of the immunopurified proteins, respectively. The phosphorylated fraction is determined by the P/WB ratio, with the ratio of the first column being the reference value. The minor band in the WB panel A is believed to be the nonglycosylated precursor form of Lu/BCAM. It is also detected in HEL-Lu cells (B) but to a lesser extent, as in Figures 3A and 5C. Typical results of 5 (A) and 4 (B) independent experiments. (C) The cytoplasmic domain of Lu and Lu(v13). Lu(v13) cytoplasmic sequence is identical for both isoforms and includes a single tyrosine residue (Y569) predicted to be at the border of the membrane and the cytoplasmic domains. The Lu 40 extra a.a. comprise the GARGGS motif (underlined) that is similar to the Akt consensus motif RXRXXS/T.