Characterization of transcription termination associated-RNAs (TTSa-RNAs): new insights into their biogenesis, tailing and expression in primary tumors

Next-generation sequencing has uncovered novel classes of small RNAs(sRNAs)in eukaryotes,in 30addition to the well-known miRNAs, siRNAs and piRNAs.In particular, sRNAspeciesarise from 31transcription start sites (TSSs) and the transcription termination sites (TTSs) of genes. However, a 32detailed characterization of these new classes of sRNAs is still lacking. 33Here we present a comprehensive study of sRNAs derived from TTSsof expressed genes (TTSa-RNAs) 34in human cell lines and primary tissues.Taking advantage of sRNA-sequencing, we show that TTSa-35RNAs are present in the nuclei of human cells, are loaded onto both AGO1 and AGO2 and their 36biogenesis does not requireDICER andAGO2 endonucleolytic activity. TTSa-RNAsdisplay a strong37bias against a G residue in the first position at 5' end, a knownfeature of AGO-bound sRNAs, and a 38peculiar oligoA tail at 3’ end.AGO-bound TTSa-RNAs derive from genes involved in cell cycle 39progression regulationand DNA integrity checkpoints.Finally, we provide evidence that TTSa-RNAs 40can be detected by sRNA-Seq in primary human tissue and their expression increases in tumor samples 41as compared to non-tumor tissues, suggesting that in the future TTSa-RNAs might be explored as 42biomarker for diagnosis or prognosis of human malignancies