Bacteriophage circular gene

The first step is the isolation of DNA genes that code for the production of the desired protein. The next stage is the insertion of these genes (foreign DNA) into a vector, or carrier. Common vectors used are the bacteriophage (a virus) and the bacterial plasmids, which are circular bacterial DNA. 

Filamentous bacteriophages. Bacteriophages of the Ff family include the fd, fl, and M13 strains.313,32-36 Phage Ml 3 is widely used in cloning genes and for many other purposes (Chapter 26). The genome is a circular, single-stranded DNA of 6400 nucleotides... 

Many plasmids and bacteriophages have been ingeniously modified to enhance the delivery of recombinant DNA molecules into bacteria and to facilitate the selection of bacteria harboring these vectors. Plasmids are circular duplex DNA molecules occurring naturally in some bacteria and ranging in size from 2 to several hundred kilobases. They carry genes for the inactivation of antibiotics, the production of toxins, and the breakdown of natural products. These accessory chromosomes can replicate independently of the host chromosome. In contrast with the host genome, they are dispensable under certain conditions. A bacterial cell may have no plasmids at all or it may house as many as 20 copies of a plasmid. 

Suitable vectors have been derived from the bacteriophage M13 which, except in its replicating form (RF), contains single-stranded circular DNA. The derivative M13 mpl, produced by insertion of part of the Escherichia coli lac operon, was mutated to give a single site for the restriction endo nuclease EcoRl within the gene for /8-D-galactosidase. This enzyme produces a blue colour when the hosts of this... 

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