1-4.3.1 Limitation of Cosmid vector:
• Slower replication
• Higher frequency of recombination inside bacterial host.
• Unstable inside E.coli host and thus easy to lose vector.
Example:
pJB8 is 5.4 kb in size and carries the ampicillin-resistance gene (ampR), a segment of λ DNA containing the cos site, and an Escherichia coli origin of replication (ori).
Fig 1-4.3.1: Schematic representation of pJB8
1-4.4 Fosmid:
• Fosmids are similar to cosmids, however they are primarily based on bacterial F-plasmid.
• Simon and co-workers, in the year 1992, first developed F-factor based vector named as pFOS for stable propagation of cosmid sized human genomic DNA inserts.
• They carry the F plasmid origin of replication and a λ cos site.
• Fosmids can carry up to 40 kb of insert DNA.
• The cloning vector is limited, as a host (usually E. coli ) can only contain one fosmid molecule. Low copy number offers higher stability as compared to high copy number cosmids.
• Fosmids have high structural stability and have been found to maintain human DNA effectively even after 100 generations of growth. It is ideal to use a fosmid vectors for constructing genomic and meta-genomic libraries.