The pSI Mammalian Expression Vector promotes constitutive expression of cloned DNA inserts in most mammalian cells. The vector is maintained as an episome in cells expressing the SV40 large T antigen, leading to even higher levels of expression. A β-globin/IgG chimeric intron located downstream from the enhancer/promoter region can further increase expression. In addition, the late SV40 polyadenylation signal increases the steady-state level of RNA approximately fivefold more than the early SV40 polyadenylation signal.
The major difference between the pCI and pSI Mammalian Expression Vectors is the enhancer/promoter region controlling expression of the inserted gene. The pSI Expression Vector contains the simian virus 40 (SV40) enhancer and early promoter region. This vector can be used for both transient and stable expression of genes. For stable expression, the pSI Vector must be co-transfected with an expression vector containing a selectable gene for mammalian cells.
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