what is Shuttle vector in gene cloning ?

What is Shuttle vector in gene cloning ?

Cloning of foreign DNA is usually carried out primarily in E.coli since the organism is most thoroughly studied. But subsequent work often requires the foreign segment to be delivered to different host cells like eukaryotes. A number of vectors are devised to satisfy this requirement. These vectors are termed as shuttle vectors. These vectors have origins of replication of various hosts. The also contain fragments of eukaryotic viruses to facilitate entry into the cell or expression or integration in the cell itself. Thus shuttle vectors allow DNA to be transferred between two different species where it can be propagated by utilizing both the origins of replication. Usually the origins of replication are derived from bacterial and eukaryotic systems. Shuttle vectors also carry antibiotic resistance genes, which are functional in eukaryotes e.g. Neomycin (G418), Hygromycin, Methotrexate etc. All the DNA manipulation and characterization are done in prokaryotic system and then the manipulated DNA is introduced into the eukaryotic systems for protein expression and functional analysis. Eukaryotic host systems are better for expression of protein for few reasons:

1. Proper folding of the protein to attain functional activity .

2. Posttranslational modification of proteins for which prokaryotes does not possess any machinery. The most conventional and convenient model system for expression of eukaryotic proteins is yeast, Pichia pastoris, which is both genetically and physiologically well characterized.