Previous studies in vivo reported that processing of primary microRNA (pri-miRNA) is
coupled to transcription by RNA polymerase II (RNAP II) and can occur co-transcriptionally.
Here we have established a robust in vivo system in which pri-miRNA is transcribed by
RNAP II and processed to pre-miRNA in HeLa cell nuclear extracts. We show that both the
kinetics and efficiency of pri-miRNA processing are dramatically enhanced in this system
compared to that of the corresponding naked pri-miRNA. Moreover, this enhancement is …