L1 Antisense Promoter Drives Tissue‐Specific Transcriptionof Human Genes

Transcription of transposable elements interspersed in the genomeis controlled by complex interactions between their regulatoryelements and host factors. However, the same regulatory elementsmay be occasionally used for the transcription of host genes. Onesuch example is the human L1 retrotransposon, which contains anantisense promoter (ASP) driving transcription into adjacent genesyielding chimeric transcripts. We have characterized 49 chimericmRNAs corresponding to sense and antisense strands of human genes.Here we show that L1 ASP is capable of functioning as analternative promoter, giving rise to a chimeric transcript whosecoding region is identical to the ORF of mRNA of the followinggenes: KIAA1797, CLCN5, and SLCO1A2.Furthermore, in these cases the activity of L1 ASP istissue-specific and may expand the expression pattern of therespective gene. The activity of L1 ASP is tissue-specific also incases where L1 ASP produces antisense RNAs complementary toCOL11A1 and BOLL mRNAs. Simultaneous assessmentof the activity of L1 ASPs in multiple loci revealed the presenceof L1 ASP-derived transcripts in all human tissues examined. Wealso demonstrate that L1 ASP can act as a promoter in vivo andpredict that it has a heterogeneous transcription initiation site.Our data suggest that L1 ASP-driven transcription may increase thetranscriptional flexibility of several human genes