The study by Taniguchi et al. (2010) investigates the protein and mRNA expression in individual *Escherichia coli* cells with single-molecule sensitivity using a newly constructed yellow fluorescent protein (YFP) fusion library. The researchers created a chromosomal YFP fusion library, where each strain has a specific gene tagged with YFP. They developed an automated imaging platform to analyze the distribution of protein and mRNA levels in single cells. Key findings include: - Protein and mRNA copy numbers vary significantly among cells, with most proteins and mRNAs present at low copy numbers. - Protein distributions can be well described by a gamma distribution, which has two fitting parameters: \(a\) and \(b\). At low expression levels, \(a\) and \(b\) have clear physical interpretations as the transcription rate and protein burst size, respectively. At high expression levels, the distributions are dominated by extrinsic noise. - A single cell's protein and mRNA copy numbers for any given gene are uncorrelated, highlighting the disconnect between the proteome and transcriptome. - The noise in protein expression scales inversely with the mean copy number at low expression levels, but at high expression levels, a plateau of ~0.1 is observed due to extrinsic noise. - mRNA noise scales inversely with the mean mRNA abundance, but the Fano factor values are close to 1.6, indicating non-Poissonian mRNA production or degradation. - The lack of correlation between mRNA and protein levels in a single cell is a general phenomenon, suggesting that extrinsic translational noise or regulatory networks must be present. - Expression parameters are correlated with gene characteristics such as codon adaptation index, GC content, and mRNA lifetime, but not with protein localization or protein-protein interactions. The study provides a quantitative and integral account of single-cell gene expression, emphasizing the need for single-cell proteome analysis to fully understand stochastic gene expression and regulation in bacteria.The study by Taniguchi et al. (2010) investigates the protein and mRNA expression in individual *Escherichia coli* cells with single-molecule sensitivity using a newly constructed yellow fluorescent protein (YFP) fusion library. The researchers created a chromosomal YFP fusion library, where each strain has a specific gene tagged with YFP. They developed an automated imaging platform to analyze the distribution of protein and mRNA levels in single cells. Key findings include: - Protein and mRNA copy numbers vary significantly among cells, with most proteins and mRNAs present at low copy numbers. - Protein distributions can be well described by a gamma distribution, which has two fitting parameters: \(a\) and \(b\). At low expression levels, \(a\) and \(b\) have clear physical interpretations as the transcription rate and protein burst size, respectively. At high expression levels, the distributions are dominated by extrinsic noise. - A single cell's protein and mRNA copy numbers for any given gene are uncorrelated, highlighting the disconnect between the proteome and transcriptome. - The noise in protein expression scales inversely with the mean copy number at low expression levels, but at high expression levels, a plateau of ~0.1 is observed due to extrinsic noise. - mRNA noise scales inversely with the mean mRNA abundance, but the Fano factor values are close to 1.6, indicating non-Poissonian mRNA production or degradation. - The lack of correlation between mRNA and protein levels in a single cell is a general phenomenon, suggesting that extrinsic translational noise or regulatory networks must be present. - Expression parameters are correlated with gene characteristics such as codon adaptation index, GC content, and mRNA lifetime, but not with protein localization or protein-protein interactions. The study provides a quantitative and integral account of single-cell gene expression, emphasizing the need for single-cell proteome analysis to fully understand stochastic gene expression and regulation in bacteria.