CiTI pre-sorting
We constructed a library of cDNA short fragments from normalized transcriptome of Hela cells to reduce abundant RNAs (like rRNAs), and inserted the library before the start codon of GFP ORF in the circRNA reporter. The resulting library were transfected into HEK294 FlpIn cells with a single reporter inserted in each clone. The cells with strong GFP signals were collected by the fluorescence-activated cell sorting (FACS), and the insertion libraries were sequenced before and after the cell sorting.