The mouse aprt promoter contains four GC boxes, which bind transcription factor Spl in vitro, and lacks both TATA and CCAAT boxes. Removal of the two most distal GC boxes of this promoter had little effect on APRT enzyme levels produced in a transient expression assay. Deletion of the distal three GC boxes resulted in a 50% reduction, and deletion of all GC boxes resulted in essentially complete loss of APRT activity. There are two predominant transcription start sites which are located within the region containing the GC boxes. The promoter behaved as a relatively strong promoter when compared to the RSV LTR promoter in a transient CAT assay, and operated in one orientation only. No upstream anti-sense transcripts were detected in either mouse CAK or liver cells, confirming that the mouse aprt promoter, unlike some other GC-rich promoters appears not to support bidirectional transcription.
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