Viruses have several features that make them good vectors. Lethal genes can be removed from viruses so that they will not kill the host cell when introduced. The deleted DNA can be replaced with DNA from other organisms. Genes necessary for infecting the host cell can be left in the virus DNA so that the ability to enter the host cell is not lost. This provides a natural method for introducing DNA into a host cell.
Viruses can accept larger genes than can plasmids.
YACs contain the origin of replication from yeast, a yeast centromere, and yeast telomere. Recombinant DNA can be inserted into host cells in a variety of ways. DNA and host cells can be combined with a solution of calcium salts. The calcium salts neutralize the charge differences between the DNA and the hosts' cell membranes and the DNA can enter the host cells. DNA can be injected into host cells with a fine pipette.