As cloning vehicles

Breeding of Vectors, (a) Plasmids. Plasmids continue to be one of the major classes of vector for cloning and amplification of DNA molecules. The most commonly used plasmids of the mid-to-late 1970 s, pSClOl and ColEl, have been modified to make them more effective as cloning vehicles. 

Physical methods of gene transfer. Genes can often be transferred without the use of a cloning vehicle. This is especially important for certain plant cells, such as those of cereal grains, for which transfer of genes via the Ti plasmid has been difficult.167 If DNA, which may be in a plasmid, is coprecipitated with calcium phosphate, it can often be taken up directly either by animal cells or by plant protoplasts.168 169 Polycations also facilitate DNA uptake cationic liposomes seem to be especially effective.170 In the widely used electroporation technique a short electrical pulse of a few hundred volts / cm is applied to create transient pores in the plasma membrane through which the DNA can enter a cell.111 8,171 175 Chromosomes can be transferred by cell fusion and either... 

Other features of the phage which add to its usefulness as a cloning vehicle are ... 

In addition to the nucleoid DNA, small circular molecules of double-stranded DNA occur in bacteria and replicate autonomously as the host cell proliferates. These are plasmids, and they carry the genes required for replication of themselves as well as for other functions, such as resistance to antibiotics. They can be readily separated from the nucleoid DNA, modified by splicing a piece of "foreign" DNA into it, and used as a vehicle for the cloning of the "foreign" DNA (Chapter 15). 

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