In bacteria, transcription and mRNA degradation take place in the same physical space, and the spatial and temporal separation between birth and death of mRNAs remains unclear. Most mRNAs have a few minutes of lifetime, and some mRNAs are known to be degraded even before they are completely transcribed. This co-transcriptional mRNA degradation has important consequences in gene regulation, yet the mechanism remains poorly understood. In particular, RNase E, which is the main ribonuclease responsible for most mRNA degradation, is localized in the inner membrane, and how RNase E performs co-transcriptional mRNA degradation remains a mystery. My group studies how RNase E performs mRNA degradation in bacteria with two different assays. First, we use single-particle tracking to measure the subcellular localization of RNase E as well as their diffusion dynamics. Second, we measure co-transcriptional and post-transcriptional mRNA degradation rates to understand how mRNA degradation is spatio-temporally regulated. I will present recent results that we obtained from these two assays.