The present invention describes the development of a
positive selection vector based on regulatory element modulation, wherein such modulation is achieved via insertional reconstruction or destruction of a regulatory element controlling transcription, translation,
DNA replication and termination. A
positive selection cloning vector pREM5Tc has been developed based on insertional reconstruction of a regulatory element of a
reporter gene. The vector pREM5Tc carries the
tetracycline resistance
reporter gene with no functional -35 region of its
promoter, a regulatory element, thus resulting in no expression of the
tetracycline resistance
gene. Hence a host
cell carrying the vector pREM5Tc is unable to produce the
tetracycline resistance
gene protein resulting in inhibition of its growth in presence of tetracycline. An E. coli
consensus -35 region is recognized as 5'-TTGACA-3' and a primer used in
polymerase chain reaction (PCR) carries at its 5' end the sequence 5'-TGTCAA-3', which is the complementary sequence of 5'-TTGACA-3'. The PCR-amplified
DNA fragment is ligated to pREM5Tc thus reconstructing the functional
promoter of the tetracycline resistance
reporter gene. Subsequent transformation of a host
cell with the recombinant vector (carrying an insert
DNA) results in production of the tetracycline resistance reporter
gene protein that confers resistance to tetracycline thus allowing only the recombinants to grow in presence of tetracycline. The
positive selection vector pREM5Tc greatly reduces, if not eliminates, the number of
exonuclease-generated false positive clones.