STAT5A/WKR inhibits the expression of the IL-3–responsive genes pim-1, cis, and osm in the myeloid cell line 32D. 32D cells expressing either the neomycin resistance gene alone (32D/Neo) or STAT5A/WKR (32D/WKR) were deprived of IL-3 for 6 hours and then stimulated with 10% WEHI-3B–conditioned medium. Total RNA was prepared at the indicated time periods and analyzed by Northern blot using ³²P-labeled PIM-1,CIS, or OSM probes. All lanes had equal loading as judged by ethidium bromide staining of ribosomal RNAs (data not shown).