Interestingly, at the exon 1 coding region and the 39 end of the exon 1 region of the GFAP gene, we also detected a second peak of activated STAT3 binding signals (primer sets e-g) in differentiated cells but not in undifferentiated NTera-2 cells (Fig. 5A ). STAT3 is a sequence-specific DNA-binding protein; in addition to the binding site at 21500 bp in the promoter (75% identities), we had identified a second binding site at +250 bp (TTCCTGGAA) at exon 1 of human GFAP (85% identities), based on a detailed sequence comparison with mouse GFAP gene. These results argue that STAT3 may originally target the binding sequence that resides at the GFAP promoter, but due to the chromatin configuration between the promoter and exon 1 in differentiated cells, STAT3 is also cross-linked to chromatin at exon 1. Alternatively, the occupancy of activated STAT3 may cause a bridge between the promoter and exon 1 which induces a stereospecific interaction on surfaces around the GFAP promoter and transcription start site.