This pKF3 DNA is a vector which is used with the enforcement cloning system. The pKF3 DNA contains chloramphenicol resistant gene and lethal gene rpsL (streptomycin-sensitive ribosomal protein) at downstream regions of the tryptophan promoter. This vector is designed for a multi-cloning site which possesses an amber mutant and 39 restriction sites on the rpsL gene; therefore, normal rpsL will not be expressed if a target gene is inserted into these restriction sites. Only targeted clones can be grown, because uninserted clones cannot be grown in trpR-, rpsL- and supE- host like E. coli TH2. Therefore, it is easy to select targeted clones.
