UCLA

MicroRNAs (miRNAs) are small, noncoding RNAs that play a vital role in gene regulation for many

biological processes by binding target transcripts and marking them for degradation or post-

transcriptional silencing. miRNAs undergo maturation within the nucleus beginning with cleavage of

primary miRNA (pri-miRNA) by Drosha/DGCR8 to form premature miRNA (pre-miRNA). Whether this

recognition relies more heavily on sequence motifs or structural features within the pri-miRNA is

unknown. Algorithms based upon these potential recognition motifs predict many more miRNA

sequences within the human genome than have been observed. To investigate the type of features that

target a sequence for miRNA processing, we conduct a library screen of miRNA sequences within

HEK293T cells to obtain a global view of miRNA processing. A reporter system consisting of GFP-P2A-

puromycin and a mCherry—pri-miRNA fusion library was utilized. Library sequences that are processed

by Drosha/DGCR8 lead to cleavage and degradation of the mCherry transcript and a decrease in

fluorescence. These sequences are then analyzed for sequence motifs or structural features to elucidate

how miRNAs are recognized and targeted for maturation.