title: LTR_L1
design: The purified RNAs were first fragmented randomly to short fragments of 150-200 bp by addition of a fragmentation buffer, then cDNA synthesis followed using random hexamers. After the first strand was synthesized, a custom second-strand synthesis buffer (Illumina), dNTPs (dUTP, dATP, dGTP and dCTP) and DNA polymerase I were added to synthesize the second-strand, then followed by purification by AMPure XP beads, terminal repair, polyadenylation, sequencing adapter ligation, size selection, and degradation of second-strand U-contained cDNA by the USER enzyme. The strand-specific cDNA library was generated after the final PCR enrichment. The concentration of the library was first quantified by Qubit2.0, then diluted to 1 ng/ul, and the insert size was checked by Agilent 2100 and further quantified by qPCR (library concentration > 2 nM). The libraries were then subjected to HiSeq sequencing according to the concentration and the expected data volume.