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Turnover of primary transcripts is a major step in the regulation of mouse H19 gene expression

In the gene expression pathway, RNA biogenesis is a central multi‐step process where both message fidelity and steady‐state levels of the mature RNA have to be ascertained. An emerging question is whether RNA levels could be regulated at the precursor stage. Until recently, because it was technically very difficult to determine the level of a pre‐mRNA, discrimination between changes in transcriptional activity and in pre‐mRNA metabolism was extremely difficult. H19 RNA, the untranslated product of an imprinted gene, undergoes post‐transcriptional regulation. Here, using a quantitative real‐time RT–PCR approach, we accurately quantify its precursor RNA levels and compare these with the transcriptional activity of the gene, assessed by run‐on assays. We find that the levels of H19 precursor RNA are regulated during physiological processes and this regulation appears to be related to RNA polymerase II transcription termination. Our results provide direct evidence that turnover of polymerase II primary transcripts can regulate gene expression in mammals.