What is meant by COS site?
“Cos” is the abbreviation of “cohesive end site”. This is a speciality of the lambda phage which has to be linearized to fit into the phages head, but circularizes in the host cell. To achieve this, it has the cohesive (or sticky) sites at each end.
What is a cos site in genetics?
Quick Reference. Cohe sive end sites, nucleotide sequences that are recognized for packaging a phage DNA molecule into its protein capsule.
What are cos sites in phage λ What is their significance?
The cos site is the region of DNA at which the lambda genome consists of a single-stranded sticky end that forms a base pair to give rise to a circular DNA when it enters the bacterial cell. The lambda phage has 12 bases hence 12 nucleotides at the cos end. These sequences are 5′ GGGCGGCGACCT 3′ and 5′ AGGTCGCCGCCC 3′.
What is cos site in plasmid?
Cosmids are plasmids that contain the λ cos, or cohesive ends, sites that are the λ sequences required for the packaging of DNA into a λ phage particle. Cosmids also contain a plasmid origin of DNA replication, at least one selectable marker, and useful restriction endonuclease sites.
How are cosmids made?
Cosmid vectors are developed by combining the features of the plasmid vector and the bacteriophage vector. Origin of replication, multiple cloning site and selectable marker are obtained from the plasmid and only the cohesive site or cos site region is taken from lambda phage.
What is cos site why it is important?
The cos site represents the junction between two genomes in a concatemer and serves as the packaging initiation site. Unlike the pac sequences of viruses that use the head-full packaging mechanism, cos also serves as a specific packaging termination sequence.
What is the difference between cosmid and plasmid?
The main difference between plasmid and cosmid is that plasmid is a loop of double-stranded DNA, naturally found in the bacterial cytoplasm and replicates independently from chromosomes whereas cosmid is a type of plasmid constructed by the insertion of cos sequences from the λ phage.
What is an advantage of cosmid over plasmid?
Cosmid Vectors Since the plasmid does not require the lambda genes necessary to form progeny phage particles on infection, there is more capacity in the cosmid for containing insert DNA than with a bacteriophage lambda vector. As a result, cosmids can generally accept 30–40 kb insert fragments.
How are cosmids constructed?
What is the function of Cos sites?
The cosB site holds the terminase while it is nicking and separating the strands. The cosQ site of next cosmid (as rolling circle replication often results in linear concatemers) is held by the terminase after the previous cosmid has been packaged, to prevent degradation by cellular DNases.
What is difference between plasmid and cosmid?
What are the advantages of using cosmids as gene vectors?
One of the advantages of cosmids for constructing genomic libraries of organisms with large genomes is that they have a cloning capacity about twice that of lambda vectors, i.e., they can accept inserts of up to about 40 kb whereas lambdas are restricted to about 20 kb.
What are the advantages of the use of a cosmid vector?
What is the purpose of Cos site in a cosmid vector?
Cos sequences are ~200 base pairs long and essential for packaging. They contain a cosN site where DNA is nicked at each strand, 12 bp apart, by terminase. This causes linearization of the circular cosmid with two “cohesive” or “sticky ends” of 12bp. (The DNA must be linear to fit into a phage head.)
