USF BINDS TO THE APB-ALPHA SEQUENCE IN THE PROMOTER OF THE AMYLOID BETA-PROTEIN PRECURSOR GENE

The APB alpha domain in the amyloid P-protein precursor (APP) promoter contains a nuclear factor binding domain with the core recognition se quence TCAGCTGAC. Proteins in nuclear extracts from brain and numerous cell lines bind to this domain and it contributes similar to 10-30% t o the basal APP promoter activity. Included in this domain is the CANN TG motif, which is recognized by basic helix-loop-helix transcription factors. The same motif is also present in the CDEI element of the yea st centromere and in the adenovirus major late promoter (AdMLP), Here we present evidence based on thermostability, relative binding affinit y, electrophoretic mobility and antibody recognition that the cellular proteins that bind to the APB alpha and CDEI motifs are USF, However, the relative binding affinity for the motifs is different, The affini ty of USF for AdMLP is similar to 20-fold higher than for the APB alph a sequence and 5-fold higher than for the CDEI sequence. Mutational an alysis suggested that the primary determinant for USF binding affinity resides within the octamer CAGCTGAC, which is composed of the E-box c onsensus sequence CANNTG followed by the dinucleotide AC, The human ho molog of the mouse CDEI binding protein did not bind to either the CDE I sequence or APB alpha.