The pSG5 Vector is a 4.1 Kb eukaryotic expression vector constructed by combining pKCR2 and the Stratagene pBS vector. The high copy number of this plasmid allows for large quantities of double-stranded DNA to be obtained. Expression in vivo is achieved via transient expression in a variety of cell lines (highest level of expression is obtained following transfection of a cell line expressing the T antigen).