Cloning Vector

Definition

• A cloning vector is a small, self-replicating DNA molecule that is used to transfer foreign genetic material into a host cell.
• It acts as a carrier for the DNA fragment of interest, allowing it to be replicated and expressed in the host.

Characteristics of an Ideal Cloning Vector

• A good cloning vector must have the following features:
  1. Origin of Replication (ori) → Enables the vector to replicate independently in the host.
  2. Selectable Marker → A gene (e.g., antibiotic resistance) that helps identify cells containing the vector.
  3. Multiple Cloning Site (MCS) → Contains recognition sites for multiple restriction enzymes to facilitate gene insertion.
  4. Small Size → Smaller vectors are easier to manipulate.
  5. High Copy Number → Ensures large-scale production of recombinant DNA.

Types of Cloning Vectors

1. Plasmids → Small, circular DNA molecules found in bacteria (e.g., pBR322, pUC19).
2. Bacteriophages (Phage Vectors) → Viruses that infect bacteria (e.g., λ phage).
3. Cosmids → Hybrid of plasmids and bacteriophage λ DNA, can carry larger DNA fragments.
4. BACs (Bacterial Artificial Chromosomes) → Used for cloning very large DNA fragments (100-300 kb).
5. YACs (Yeast Artificial Chromosomes) → Used for cloning extremely large DNA fragments (up to 1000 kb).

Examples of Cloning Vectors

• pBR322 → One of the first widely used plasmid vectors, contains ampicillin and tetracycline resistance genes.
• pUC19 → A high-copy-number plasmid with a lacZ marker for blue-white screening.

λ Phage → Can carry larger DNA fragments than plasmids.

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