A novel isothermal method for amplification of long specific amplicon from linear template

Isothermal nucleic acid amplification methods have been successfully developed and applied for diagnostic purpose, especially for detection of pathogens. However, amplicon size of such methods is relatively short (< 500 bp) to limit their application for long amplicon production that can be used for various downstream applications including genomic surveillance of pathogens. To fill the gap, we developed a method for specific amplification of kilobases-long target sequence from RNA templates. This method, named CREA, utilizes sequence specific recombination of Cre recombinase to generate circular intermediate template for subsequent RCA reaction. CREA with SARS-CoV-2 spike template could amplify ~ 2.9 kb target and up to ~ 1.9 kb amplicon was able to produce in sufficient amount for general cloning. Each step of CREA procedure was thoroughly analyzed to provide directions for further optimizations. Furthermore, we evaluated a variation of CREA which utilized DNA ligase.