Cosmid

brief discription of cosmid vector for net ,set ,m.sc,b.sc exams

1. Cosmid

2. Cosmids are medium sized cloning vectors. The cloning capacity of these vectors is 35-45 kbp. Cosmid vector are developed by combining the features of plasmid vector and bacteriophage vector. The first cosmid vector was described by Collins in 1978.

3. In Brief A cosmid is a plasmid that contain phage sequence that allows the vector to be packaged and transmitted to bacteria like phage vector. Or A cosmid is a type of hybrid plasmid that contains a Lambda phage cos sequence. Cosmids ( cos sites + plasmid = cosmids ) DNA sequences are originally from the lambda phage.

4. Plasmid A plasmid is a small DNA molecule within a cell that is physically separated from a chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria. plasmids are sometimes present in archaea and eukaryotic organisms.

5. Lambda genome A linear DNA molecule, has a 12 base long , single stranded complementary overhang at both ends. Which emerge during the packaging process into phage particle through splitting of cos site.

6. Features of plasmid Origin of replication Multiple cloning site Selectable marker Features of lambda phage Only cohesive site or cos site region

7. Properties of cosmid vector These are fused together to obtain the cosmid vector approximately 200 bp lambda sequence is cloned into cosmid vector. A cosmid vector may have one or two cos site. Cosmid vector are used in construction of genomic libraries. Cosmid vector have cloning capacity up to 45 kbp.

8. Cloning of foreign DNA in cosmid vector involves the following steps Ligation of foreign DNA between two cos site. Making a concatemeric DNA. Invitro packaging to introduce the DNA into phage head to form the matured phage particle. Introduction of the cloned DNA into E.coli by transduction. After their entry into host cell the cosmid are maintained as plasmid.

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