Vectors are DNA molecules that can carry foreign DNA. There are two main types of vectors: cloning vectors are used to increase copies of cloned DNA fragments, while expression vectors are used to express foreign genes as proteins. Ideal vectors are autonomously replicating, contain antibiotic resistance markers, and have unique restriction sites. Common vector types include plasmids, which can clone fragments up to 10kb; bacterial artificial chromosomes for 35-300kb inserts; and yeast artificial chromosomes for 100-1000kb inserts. The choice of vector depends on the size of the DNA fragment to be cloned and the intended host organism.

1. Vectors (Cloning Vectors)
Definition:
Vector is an autonomously replicating (inside a host cell) DNA molecule designed from a
plasmid or phage DNA to carry a foreign DNA inside the host cell. Transformation vectors
are of two types:
 Cloning vector is used increasing the number of copies of a cloned DNA fragment.
 Expression vector is used for expression of foreign gene into a protein.
 If a vector is designed to perform equally in two different hosts, it is called a shuttle
vector.
Properties ofan ideal vector:
 Autonomously replicating i.e. should have ori (origin of replication) region.
 Contain at least one selectable marker e. g. gene for antibiotic resistance.
 May contain a scorable marker (β -galactosidase, green fluorescent protein etc.)
 Presence of unique restriction enzyme site.
 Have multiple cloning sites.
 Preferably small in size and easy to handle.
 Relaxed control of replication to obtain multiple copies.
 Presence of appropriate regulatory elements for expression of foreign gene.
 High copy number
The selection of a suitable vector system depends mainly on the size limit of insert DNA
and the type of host intended for cloning or expression of foreign DNA.
Typesof cloning vectors:
1. Plasmid – The size of a plasmid is 4361 bp, and the cloning limit is 0.1-10 kb. The marker
gene is ampicillin and the tetracycline resistant gene whereas it remains isolated from the
E.Coli. Example: PBR322

2. 2. Bacterial Artificial Chromosome – The size of BAC is 11827 bp and the cloning limit is 35-
300 kb. The marker gene is chloramphenicol and lactose metabolizing gene. It is a
modification of f-plasmid and is artificially synthesized. Example: pUvBBAC
3. Yeast Artificial Chromosome – The size of YAC is 11400 bp and the cloning vector 100-1000
kb. The marker is similar to that of yeast. It is artificial and has yeast centromere, which is
isolated from the Saccharomyces cerevisiae.
4. Λ Bacteriophase – Its size is 48502 bp and 1/3rd of this is not essential. It can only
recombinant about 4-5 kbp of the donor DNA. An example is lambda genome.
6. Cosmid – The size of cosmid is 7900 bp and the cloning limit is 30-50 kb. It has features
similar to both phase and plasmid and an example of it is super COS1
7. Human Artificial Chromosome – It is an artificial chromosome that is used to transfer
human gene and has no limit on cloning as it can carry a large segment of the DNA.
Name Size Cloning limit Marker gene Example
Plasmid 4361 bp 0.1-10 kb Ampicillin and
tetracycline
PBR322
Bacterial
artificial
Chromosome
11827 bp 35-300 kb chloramphenicol
and lactose
metabolizing gene
pUvBBAC
Yeast Artificial
Chromosome
11400 bp 100-1000 kb Similar to yeast –
Bacteriophase 48502 bp – – Lambda
genome
Cosmid 7900 bp 30-50 kb – COS1

3. Human Artificial – No limit – –
Cloning Vectors Usedin Genetic Engineering
 1973 Plasmid
 1974 -Bacteriophage lambda
 1977- Plasmid pBR322
Bacteriophage M13 (M13 mp1)
 1978- Cosmid
 1987 -Yeast artificial chromosome-YAC
 1990 -Bacteriophage P1
 1992 -Bacterial artificial chromosomeBAC
 1994 -P1 artificial chromosome- PAC
 1997- Human artificial chromosome-HAC
 2007 -Maize mini-chromosomes

4. Steps involved in gene cloning