Introduced in living E. coli cells, the SPP (Single Protein Production) System exploits the properties of MazF, a bacterial toxin that is an ssRNA- and ACA-specific endoribonuclease. Expression of this nuclease along with an engineered ACA-less target protein enables high signal to noise ratios. For improved protein solubility and stability, it utilizes the promoter derived from cspA gene, one of the cold-shock genes. It is suitable for structural analysis of proteins by NMR, as it allows for nearly exclusive labeling of the target protein (15N and 13C for NMR). Proteins that are toxic or tend to easily aggregate when expressed at high level can also be obtained using the system.