In order to clone PCR products and express them effectively in Escherichia coli, a directional
cloning system was constructed by generating a T vector based on pQE-30Xa. The vector
was prepared by inserting an XcmI cassette containing an endonuclease XcmI site, a kanamycin
selective marker, a multiple-cloning-site (MCS) region and an opposite endonuclease
XcmI site into the vector pQE-30Xa. The T vector pQE-T with single overhanging dT residues
at both 3′ ends was obtained by digesting with the restriction enzyme XcmI. For
directional cloning, a BamHI site was introduced to the ends of the PCR products. A BamHI
site was also located on the multiple cloning site of pQE-T. The PCR products were ligated
with pQE-T. The directionally inserted recombinants were distinguished by using BamHI
to digest the recombinants because there are two BamHI sites located on the both sides
of PCR fragment. In order to identify the T-vector functions, the 14-3-3-ZsGreen and hRBP
genes were amplified and a BamHI site was added to the ends of the genes to confirm this
vector by ligation with pQE-T. Results showed that the 14-3-3-ZsGreen and hRBP were cloned
to the vector pQE-T directly and corresponding proteins were successfully produced. It was
here demonstrated that this directional vector is capable of gene cloning and is used to
manipulate gene expression very easily. The methodology proposed here involves easy incorporation
of the construct into other vectors in various hosts