Turnover of JAK2 protein. MedB-1 and L428 cells were pulsed with ³⁵S-methionine/cysteine for 30 minutes and chased for the times indicated. Cell protein extracts were used for immunoprecipitation with anti-JAK2 antibodies and subjected to SDS-PAGE and autoradiography. (A) Details of the x-ray films. (Top) ³⁵S-JAK2 signals obtained from MedB-1 protein extracts indicating degree of synthesis (0 hours) and dynamics of degradation. (Bottom) Signals obtained from an experiment with L428 cells after. (B) Time-dependent degradation of JAK2 in MedB-1 (▪) and L428 cells (). Intensities of the bands were analyzed using the ImageMaster VDS hardware and software, and the integrated optical densities of the bands at time zero were set as 100% synthesis.