E. coli strains for in vitro studies

The E. coli strain Rosetta (DE3) was used to express Pif1 protein. The E. coli strain BL21 (DE3) was used to express RPA and all other helicase proteins. These e. coli cells were incubated at 37°C in LB medium for 4 h, and then the protein expression was induced by IPTG at 18°C for 16 h.