STAT5A/B binding sites in a putative Tfr1 enhancer. (A) Putative STAT5A/B binding (GAS) sites within intron 1 of the Tfr1 gene (underlined). Three conserved GAS sites were identified, with GAS 1 having the highest interspecies conservation. Sites are shown aligned with sequences from other species.²¹  (B) Chromatin immunoprecipitation (ChIP) analysis of binding of active STAT5A to the putative GAS sites within intron 1 of Tfr1. Biologic and technical triplicates were performed. Error bars represent SEM. *P < .05 compared with GFP-transfected cells.