Repeat-length-independent broad-spectrum shuffling, a novel method of generating a random chimera library in vivo

We describe a novel method of random chimeragenesis based on highly frequent deletion formation in the Escherichia coli ssb-3 strain and a deletion-directed chimera selection system that uses the rpsL⁺ gene as a reporter. It enables the selection of chimeras without target gene expression and can therefore be applied to cytotoxic targets. When this system was applied to phospholipase D genes from Streptomyces septatus TH-2 and Streptomyces halstedii subsp. scabies K6 (examples of cytotoxic targets), chimeragenesis occurred between short identical sequences at the corresponding position of the parental genes with large variations. Chimeragenesis was >1,000 times more frequent in the ssb-3 background than in the ssb ⁺ background. We called this system repeat-length-independent broad-spectrum shuffling. It enables the convenient chimeragenesis and functional study of chimeric proteins. In fact, we found two amino acid residues related to the thermostability of phospholipase D (Phe426 and Thr433) by comparing thermostability among the chimeric enzymes obtained.