XACT-seq: A photocrosslinking-based technique for detection of the RNA polymerase active-center position relative to DNA in Escherichia coli .

XACT-seq ("crosslink between active-center and template sequencing") is a technique for high-throughput, single-nucleotide resolution mapping of RNA polymerase (RNAP) active-center positions relative to the DNA template. XACT-seq overcomes limitations of approaches that rely on analysis of the RNA 3' end (e.g., native elongating transcript sequencing) or that report RNAP positions with low resolution (e.g., ChIP-seq and ChIP-exo). XACT-seq can be used to map RNAP active-center positions in transcription initiation complexes, initially transcribing complexes, and transcription elongation complexes. For complete details on the use and execution of this protocol, please refer to Winkelman et al. (2020).