PRO‐seq: Precise Mapping of Engaged RNA Pol II at Single‐Nucleotide Resolution

Abstract Gene regulation is dependent on the production of mRNAs and a repertoire of non‐coding RNAs by RNA polymerase II (RNAPII). Precision run‐on sequencing (PRO‐seq) maps the position of engaged RNAPII complexes at single‐nucleotide resolution and can reveal direct targets of regulation, locations of enhancers, and transcription mechanisms that are difficult or impossible to measure by analysis of total cellular RNA. Briefly, this method first involves permeabilizing cells with mild detergents to remove intracellular NTPs and halt transcription. Transcription is then resumed in the presence of biotin‐NTPs and sarkosyl to allow transcriptional incorporation of a single biotinylated NTP by RNAPII. The biotin moiety is then bound to streptavidin beads to stringently enrich for nascent RNAs. Sequencing libraries are then generated such that the first base read corresponds to the 3′ end of the nascent transcript. Here, we describe our current protocol for generating PRO‐seq libraries from metazoan cells, including adaptations of previously published protocols to incorporate unique molecular identifiers, reduce ligation bias, and improve library yields. Additional commentary describes quality control and processing of PRO‐seq data and references for more advanced downstream analysis such as gene and enhancer identification. © 2023 Wiley Periodicals LLC. Basic Protocol 1 : Cell permeabilization for PRO‐seq Basic Protocol 2 : Construction of PRO‐seq libraries Support Protocol : Adenylation of 3′ adapter