The pTARGET™ Mammalian Expression Vector System(a,c) is a convenient system
for cloning PCR(b) products and for expression of cloned PCR products in mammalian
cells. The vector is prepared by cutting the pTARGET™ Vector with EcoR V
and adding a 3´ terminal thymidine to both ends. These single 3´-T overhangs at the
insertion site greatly improve the efficiency of ligation of a PCR product into the plasmid
in two ways. First the overhangs prevent recircularization of the vector; secondly
they provide a compatible overhang for PCR products generated by certain thermostable
polymerases (1,2). As summarized in Table 1, these polymerases often
add a single deoxyadenosine in a template-independent fashion to the 3´-ends of
amplified fragments (3,4). The pTARGET™ Vector also contains a modified version of
the coding sequence of the α-peptide of β-galactosidase, allowing blue/white recombinant
screening.
The pTARGET™ Vector carries the human cytomegalovirus (CMV) immediate-early
enhancer/promoter region(c) to promote constitutive expression of cloned DNA
inserts in mammalian cells. This vector also contains the neomycin phosphotransferase
gene, a selectable marker for mammalian cells. The pTARGET™ Vector can be
used for transient expression or for stable expression by selecting transfected cells
with the antibiotic G-418.