SV40 virus expression vectors.

SV40 late-replacement vectors provide an excellent means for expressing large amounts of proteins from cDNAs of less than 2400 bp. The amount of protein made 28 hr after infection is sufficient for extremely brief pulse-chase protocols. At periods postinfection when cells are still healthy, sufficient protein has been made for techniques in which only a small fraction of the protein is detected, including immunocytochemistry on cryosections. Because of the ease of subcloning DNA fragments into them, the ease of making virus stocks, and the ability to achieve comparable amounts of protein expression reproducibly with different infections, these vectors are superb tools for comparing series of mutants made by site-directed mutagenesis, especially if a normal cellular environment is important for the measurements to be made.