FLANKING SEQUENCES OF AN ALU SOURCE STIMULATE TRANSCRIPTION IN-VITRO BY INTERACTING WITH SEQUENCE-SPECIFIC TRANSCRIPTION FACTORS

An Alu source gene, called the EPL Alu, was previously isolated by a p hylogenetic strategy. Sequences flanking the EPL Alu family member sti mulate its RNA polymerase III (Pol III) template activity in vitro. On e cis-acting element maps within a 40-nucleotide region immediately up stream to the EPL Alu. This same region contains an Ap1 site which, wh en mutated, abolishes the transcriptional stimulation provided by this region. The flanking sequence, as assayed by gel mobility shift, form s sequence-specific complexes with several nuclear factors including A p1. These results demonstrate that an ancestral Alu source sequence fo rtuitously acquired positive transcriptional control elements by inser tion into the EPL locus, thereby providing biochemical evidence for a model which explains the selective amplification of Alu subfamilies.