Gene Bridges FLPe expression plasmids enable FLP-mediated site-directed recombination in E. coli, and are propagated at 30C in low copy number. The flpe gene is driven by the lambda-R promoter and is under control of the heat labile cI857 repressor. A temperature upshift from 30C to 37C results in transient FLPe recombinase expression. Since the expression plasmids are no longer replicated at 37C due to their pSC101 origin of replication they finally get lost. FLPe has an improved thermostability and shows enhanced recombinase activity at 37