ИСТИНА

The long 5’-untranslated region (5’-UTR) of the human retrotransposon LINE1 (L1) harbors a unique internal promoter which provides it a relative autonomy from the genomic environment. According to common opinion, the first 100-150 nt of the L1 5’-UTR are crucial to drive transcription (and thus constitute a “minimal promoter”) of this mobile element. We show that activity of the “minimal promoter” is rather poor in comparison with the entire 5’-UTR. Morover, the internal region of the 5’-UTR (+390 - +662) containing multiple binding sites for various transcription factors has proved to be an indispensable part for the effective transcription. This region may be considered as a transcriptional enhancer. Deletion of this segment leads to a dramatic loss of transcription level irrespectively of cell type, while deletion of the first 100 nt decreases the transcription efficiency no more than 2-fold. Also, the internal region of the L1 5’-UTR is able to strongly enhance the transcription activity of the minimal promoter from the ectopic site in both orientations. According to this new data, the organization of the L1 regulatory region seems much more similar to that of well-studied invertebrate LINE elements than it was thought before.