Fig. 5
Schematic presentation of the PST-SPP system. PrS, a major spore-coat protein from Myxococcus xanthus, was directly repeated (PrS2) and used as a tag (PST tag) for higher expression and solubilization of a target protein. Functional assay for the target protein can be done without cleaving the PrS2 from the fusion protein. A codon optimized ACA-less gene for the target protein can be expressed together with pACYCmazF, cleaving the ACA sequences in mRNAs, allowing the cells to produce the only target gene from its ACA-less mRNA (the SPP system; Suzuki et al. 2005). Note that the gene for PrS2 is also codon-optimized for E. coli and designed to be ACA-less without altering the amino acid sequence. Since the PrS2 tag partially suppresses the antimicrobial activity of a cloned peptide or protein, the use of the PST-SPP system allows one to produce toxic peptides and proteins in E. coli and also to perform their functional assay using the cell lysate