COMPARISON OF THE PROMOTERS OF THE MOUSE (APEX) AND HUMAN (APE) APURINIC ENDONUCLEASE GENES

We investigated the minimal promoter of APEX, which encodes mouse apur inic DNA repair endonuclease. A 1.85-kb fragment with APEX upstream se quences and similar to 290 bp of the transcribed region linked to a ch loramphenicol acetyltransferase (CAT) reporter gene was assayed by tra nsient transfection in NIH-3T3 cells. The minimal APEX promoter was co mprised of similar to 190 bp of upstream and similar to 170 bp of tran scribed DNA (exon 1 and most of intron 1). This similar to 360-bp regi on contains two CCAAT boxes and other consensus protein binding sites, but no TATA box. Deletion of the 5'-most CCAAT box decreased activity similar to 5-fold. The second CCAAT box (situated in exon 1) may play an independent role in APEX expression. Transcription start sites hav e been identified downstream of the second CCAAT box, and DNase I foot printing demonstrated NIH-3T3 nuclear proteins binding this region, in cluding an Sp1 site located between the CCAAT boxes. Electrophoretic m obility-shift assays indicated binding by purified Sp1. Mouse proteins did not bind three myc-like (USF) sites in the APEX promoter, in cont rast to the APE promoter. The APEX and APE promoter had similar activi ty in Hela cells, but in mouse cells, the murine promoter had similar to 5-fold higher activity than did the human promoter, Both the APEX a nd APE promoters exhibited bidirectional activity in their cognate cel ls. (C) 1997 Elsevier Science B.V.