CLONING VECTORS are DNA molecules that carry a foreign DNA segment and replicate inside the host cell. The most commonly used vectors are plasmids and bacteriophages.
PROPERTIES OF A GOOD VECTOR:
1. IT SHOULD HAVE AN ORIGIN OF REPLICATION [ ORI ]- It is required for replication of vector during cell division.
2. IT SHOULD HAVE SELECTABLE MARKER GENES- It is required for the identification of transformed cells from non-transformed cells. Usually, antibiotic resistance genes such as ampicillin and tetracycline resistance genes are used as selectable markers.
3. CLONING SITES- At least one unique restriction site is present on the marker gene, which can be used to insert the alien DNA.
4. CONTROL ELEMENTS- It should have control elements like PROMOTER, OPERATOR, RIBOSOMAL BINDING SITE.
Naturally occurring plasmids do not have all these properties, so Artificial plasmids are constructed.
eg. pBR-322, pBR-320, pACYC-177.
VECTORS FOR CLONING IN PLANTS AND ANIMALS:
Agrobacterium tumefaciens is a pathogen causing CROWN GALL disease in dicot plants. These bacteria possess Ti plasmid [ Ti - tumor-inducing ] containing T DNA ... T DNA is a piece of DNA required for insertion of plasmid in plant DNA.
Ti plasmid can be used as a vector to insert ALIEN DNA in plant cells.
RETROVIRUSES can be used to transfer ALIEN DNA in animal cells.
