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6.04.2007

Bacteriophage

Bacteriophages are bacteria viruses.
When they infect their host they use host machinery to replicate their DNA.

In bacteriophage vectors part of the phage DNA is replaced by the gene of interest (max. size is 15-25 kbp)

When this new recombinant phage DNA infects a host the gene of interest will be replicated.

commonly used phage vectors include M13 and λ.
Infection of bacterial cell:

Tail sticks to the cell wall

DNA from head is squired into bacteria

Phage genes are transcribed by bacterial RNA polymerase

Corresponding mRNA is translated using bacterial machinery

Newly replicated phage DNA and head and tail protein ensemble spontaneously

Lyses of host bacteria results in formation of plagues.

• l phage – most common vector for construct of genomic DNA
• Cosmid vector – can accumulate up to 45 kb
– a cross between a plasmid and l vector
– contains antibiotic resistance genes and Ori for replication in bacteria
– Contains cos sites to be packed in phage particles
– Inside of bacteria, the cosmid DNA circularizes and replicates as a large plasmid

• YAG yeast artificial chromosome , up to 200 to 500 kb
– Large DNA fragments are inserted into yeast DNA sequence and introduced into yeast cell by transformation

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