RNA-POLYMERASE-III PROMOTER AND TERMINATOR ELEMENTS AFFECT ALU RNA EXPRESSION

Promoter elements derived from the 7SL RNA gene stimulate RNA polymera se III (Pol III) directed Alu transcription in vitro, These elements a lso stimulate expression of Alus transfected into 293 cells, but trans cripts from these same constructs are undetectable in HeLa cells. A te rminator resembling the terminator for the 7SL RNA gene has no effect on in vitro Alu template activity, but increases expression in vivo in a position independent manner. Alu transcripts generated from templat es with and without this terminator have identical half-lives, indicat ing that this terminator stimulates expression by increasing template activity. Together, these results show that Alu expression may be regu lated at multiple levels and can respond to cis-acting elements. This new found ability to express Alu transcripts by transient transfection provides an opportunity to monitor their post-transcriptional fate, P rimary Alu transcripts are not extensively adenylated or deadenylated following transcription, but are short-lived compared to 118 nt scAlu RNA, In addition to Alu RNA, transfected templates encode scAlu RNA, b ut very high levels of Alu RNA expression does not increase the abunda nce of scAlu RNA, ScAlu RNA is not merely a transient RNA degradation product, but is instead tightly regulated by factors other than the ab undance of primary transcripts.