THE INITIATOR ELEMENT AND PROXIMAL UPSTREAM SEQUENCES AFFECT TRANSCRIPTIONAL ACTIVITY AND START SITE SELECTION IN THE AMYLOID BETA-PROTEIN PRECURSOR PROMOTER

The TATA-less human amyloid beta-protein precursor promoter contains a n initiator element with the sequence CGTCA(+1)GTT. Primary transcript ional start sites were identified at positions +1 and -4, Deletion of the upstream activator elements APB beta and APB alpha did not affect the selection of transcriptional start sites, although total transcrip tional activity was reduced both in vitro and in vivo. Mutations withi n the initiator element shifted the transcriptional start sites and re duced transcriptional activity. Mutations between positions -6 and -35 changed the relative utilization of start sites +1 and -4 without aff ecting the total level of transcriptional activity, A 10-base pair del etion between position -40 and -31 increased in vitro transcriptional activity with a preeminent utilization of the start site at position - 4. In contrast, a 20-base pair deletion between position -40 and -21. resulted in a reduction in transcriptional activity and in the primary utilization of the start site at position +1. Furthermore, transactiv ation by APB beta and APB alpha was eliminated. DNase I footprinting p rovided evidence for the existence of two binding domains designated U E (position -12 to -30) and Inr (position +7 to -7). The positions of these binding domains are altered in mutations and deletions that affe ct transcriptional activity.