Non-replicating vectors

These vectors do not replicate. They only serve as vehicles of transfecting DNAs which may become intetrated into the host DNA such vectors are therefore also called passive transfecting vectors. These vectors are generally shuttle vectors. THey are first cloned in E. coli to isolate recombinant vectors and then used to transfect various mammalian cells since they need not be restricted to monkey cells in view of their lack of replication. The Sv40 segments used tin these vectors are generally the transcription regulatory sequences and the polyadenylation sites. Permanent transformants are selected on the basis of selectable markers present in the vector.
The selectable marker need not be convalently linked to the DNA insert or the transfecting DNA. Even when two seperate DNA fragments containing seperate each are mixed and used for for transfection more than 50% of the permanently transfected cells contain both the genes usually integrated side by side the two DNA fragments tend to become joined after entering the animal cells which is the reason for their co-transduction i.e integration of the two genes together in the genome.