Cosmids, Phages, and plasmids as DNA carriers

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Cosmids, Phages, and plasmids as DNA carriers
Plasmid
Phage
Cosmid
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12kb-20kb
lt12 kb, can not be packaged efficiently gt20 kb,
too large to fit into the phagehead
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Cosmids as the DNA carriers
Colonies No plaques
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Cosmids as the DNA carriers
Cosmids behave both as plasmids and as
phages They contains the Cos ends from the ?
phage DNA Allow the DNA to be packaged into ?
phage heads
They also contain a origin of replication from
the plasmid so they replicate like plasmid in
bacteria
Host E. coli Vector size usually about 5-7
kb. Insert size up to 50kb
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Partial restriction digestion
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Genomic Library
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Construction of genomic libraries
Insert size gt12kb but lt20kb
Human genome 3x109 bp Hunan genomic library
Need 150,000-250,000 l phage clones to cover the
whole human genome
If plasmids are used to make the human genomic
library, 1-4 million plasmid clones are needed to
cover the whole human genome
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How do you find the gene of your interest in
genomic library? Library screening
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Hybridization
The process of annealing a DNA strand with a
complementary or nearly complementary RNA strand
or DNA strand from a different origin.
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Screening a genomic library
DNA hybridization
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