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 Xcm