JAK3 signals through JAK1 in CMK cells. (A) CMK cell lysates were immunoprecipitated with antibodies specific for JAK1 or JAK3 and subjected to immunoblot analysis for JAK1 and JAK3. (B) CMK cells were incubated with siRNA targeting JAK1, JAK2, JAK3, and TYK2 and electroporated as in (1A). After 48 hours, cell lysates were analyzed by immunoblot using antibodies specific for total and phospho-JAK1 and JAK3. (C) CMK cells were incubated with siRNA targeting JAK1 and treated as in Figure 1A. After 48 hours, cell lysates were subjected to immunoblot analysis for JAK1 and total and phospho-STAT5.