ABSTRACT
The gene constructs used for transgenesis must sometimes contain such sequences If origins of replications are really so numerous in mammalian genomes. useful. The efficiency of transgenesis may be so high with such vectors that animals, even unable to transfer them to their progeny, would be of interest. Such vectors might even have the advantage of being not transmitted. From a biosafety point of view, the fact that they are shuttle structures capable of being transmitted from mammals to bacteria and back may also create serious biorisks for the environment. Quiescent or slowly growing cells seem unable to keep this kind of gene construct. Most likely, centromeric sequences or other DNA sequences having equivalent properties should be added to the plasmid already containing origins of replication.
