The TOP10F´ genotype is identical to TOP10 with the addition of an F´ episome. The F´ episome carries the tetracycline resistance gene and allows isolation of single-stranded DNA from vectors that have an f1 origin of replication. In addition, the F´ carries the lacI^q repressor for inducible expression from trc, tac, and lac promoters using IPTG. TOP10F´ require IPTG induction for blue/white color screening.