In-vivo quantification of primary microRNA processing by Drosha with a luciferase based system

► Posttranscriptional regulation of miRNA processing is difficult to quantify. ► Our in-vivo processing assay can quantify Drosha cleavage in live cells. ► It is based on luciferase reporters fused with pri-miRNAs. ► The assay validates the processing defect caused by a mutation in pri-16-1. ► It is a sensitive method to quantify pri-miRNA cleavage by Drosha in live cells.