tokens: The 5 ' flanking region contains potential binding sites for TATA - binding protein , Sp1 , nuclear factor 1 ( NF1 ) , CAAT - box binding protein ( C / EBP ) , hepatocyte nuclear factors 1 and 5 ( HNF1 , HNF5 ) and activator proteins 1 and 2 ( AP1 , AP2 ) .