Measurements of Rate of Transcription in Isolated Nuclei by Nuclear Run-Off Assay

Unlike gene expression in prokaryotic cells, which is primarily under transcriptional control, gene expression in eukaryotic cells is subject to both transcriptional and post-transcriptional controls. Since transcription and translation in eukaryotic cells are separated topographically, the regulation of mRNA metabolism can occur at multiple sites, within nuclei and in the cytoplasm. Nevertheless, transcription remains a critical locus of control of eukaryotic gene expression. Transcriptional regulation affects cellular mRNA abundance by affecting rates of transcription. Another important control mechanism that can affect mRNA abundance is the rate of mRNA decay. Thus, steady-state levels of mRNA represents a balance between the rates of transcription and intracellular degradation, e.g., an increase in the abundance of mRNA could result from decreased mRNA degradation, increased mRNA synthesis, or both.