Prem: a positive selection vector system for direct pcr cloning

Abstract

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 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.