Comparisons of the persistence of STAT tyrosine phosphorylation induced in sensitive (D_W^S) or resistant (D_W^R) Daudi cells continuously exposed to IFN-α (100 U/mL). As in Fig 1, STATs-pTyr were disclosed by IP and 4G10 Western blots developed with ECL substrate. (A) STAT5b-pTyr (92 kD) began to decrease after 1 hour both in sensitive (D_W^S) and resistant (D_W^R) cells. Anti-STAT5b was localized by ECL. (B) STAT3-pTyr (89 kD), as indicated in Fig 1, was more strongly phosphorylated in sensitive (D_W^S) than in resistant (D_W^R) cells, but, nevertheless, had declined in each cell line by 6 hours. Anti-STAT3 was localized by ECL. (C) STAT2-pTyr (113 kD) and STAT1-pTyr (91 kD) persisted for more than 24 hours in D_W^S cells, but decreased in D_W^R cells by 8 hours. Total latent and phosphorylated STATs were assessed by reprobing of transfer membranes with specific anti-STAT antibodies and secondary detection by ECL (STAT5b, STAT3) or phosphatase substrate reaction (STAT2, STAT1).