ИСТИНА

Retroelements comprise a considerable fraction of human genome. Human endogenous retroviruses are thought to be remnants of ancient retroviral infections of human ancestors’ germ cells. HERVs can modify expression of host cell genes through their cis-regulatory elements concentrated in their long terminal repeats (LTRs). Although numerous HERV-related RNAs were identified in the human transcriptome, for most of them it remained unclear whether they are LTR-promoted or readthrough products. For transcriptome-wide quantitative and qualitative detection of the HERV-K (HML-2) LTRs promoter activity, we developed a new technique called GREM (Genomic Repeat Expression Monitor), which may be applied to genome-wide isolation and quantitative analysis of any kind of transcriptionally active repetitive elements [2]. In our experiments we found that at least 50% of the human specific HERV-K (HML-2) LTRs are promoter active in human tissues, and identified 65 novel human specific promoters. We used a 5’ RACE (rapid amplification of cDNA ends) technique to identify transcriptional start sites of LTR-promoted transcripts for human specific HERVs (HS HERVs) [1]. We have found that in addition to canonical promoter located within the U3 region of the LTR, HS HERVs also utilize an alternative transcription start site located on the border of the R and U5 LTR regions. Human retroelements L1 are believed to be the only group of autonomous transposable elements currently active in humans. About 800 bp-long 5’-untranslated region (5’-UTR) of the human L1 harbors a unique internal transcriptional promoter. There are two opinions about which part of the 5’- UTR is the most important for its functional activity: either it is the first 5’ 100-150 bp-long region [3] or it is the internal region of the 5’-UTR (+390…+662) [4]. We experimentally check these hypotheses using a reporter construct assay.