Preparation of Mammalian Nascent RNA for Long Read Sequencing

Long read sequencing technologies now allow high‐quality sequencing of RNAs (or their cDNAs) that are hundreds to thousands of nucleotides long. Long read sequences of nascent RNA provide single‐nucleotide‐resolution information about co‐transcriptional RNA processing events—e.g., splicing, folding, and base modifications. Here, we describe how to isolate nascent RNA from mammalian cells through subcellular fractionation of chromatin‐associated RNA, as well as how to deplete poly(A) + RNA and rRNA, and, finally, how to generate a full‐length cDNA library for use on long read sequencing platforms. This approach allows for an understanding of coordinated splicing status across multi‐intron transcripts by revealing patterns of splicing or other RNA processing events that cannot be gained from traditional short read RNA sequencing.