06-20-2014, 11:16 PM
Hybrid Vectors
Plasmids and phages are “regular” types of vectors that have not been heavily modified. However, the advancements in our technology and the need for more complex genetic experiments have led us to create new, improved vectors. This is due to several reasons. First of all, genetic experiments started shifting from cloning of single or several genes to the cloning of whole genomes. Secondly, cloning procedures have been commercialized to make them more available for “regular folks” through cloning kits. Nowadays, you don’t have to be awesome scientist in order to perform some decent genetic experiment (if you have the money, that is).
Some of the new vectors developed for engineering purposes are also hybrid vectors. These vectors, like cosmids or phagemids, incorporate features from different vector types (from plasmids and phages, in the case of cosmids and phagemids).
Cosmids
These are vectors made of plasmid sequences joined up by phage cos sites. Cos site represents several bases at both ends of the linear phage genome that are complementary and are able to circularize its DNA once it is inserted into the host cell (they are essentially sticky ends). The base of cosmid vectors is really small (around 4-6 kb) allowing them to accept relatively large amount of exogenous DNA (up to around 45 kb). Since they do not really have phage genes, they behave as plasmids, except that their insertion mechanism is the one from lambda phage. Basically, they are very efficient and are able to take a lot of foreign DNA, but they need more complicated procedures and their cloned sequences need further processing.
Phagemids
These hybrid vectors are based on the phages, giving them some advantages over cosmids by utilizing phage functions. Basically, they have f1 origin of replication “borrowed” from the f1 filamentous phage (it is in the same group as the phage M13). They are somewhat better because they have the ability to excise cloned DNA fragments in vivo as part of a plasmid, which removes the need for further processing of cloned sequences.
Plasmids and phages are “regular” types of vectors that have not been heavily modified. However, the advancements in our technology and the need for more complex genetic experiments have led us to create new, improved vectors. This is due to several reasons. First of all, genetic experiments started shifting from cloning of single or several genes to the cloning of whole genomes. Secondly, cloning procedures have been commercialized to make them more available for “regular folks” through cloning kits. Nowadays, you don’t have to be awesome scientist in order to perform some decent genetic experiment (if you have the money, that is).
Some of the new vectors developed for engineering purposes are also hybrid vectors. These vectors, like cosmids or phagemids, incorporate features from different vector types (from plasmids and phages, in the case of cosmids and phagemids).
Cosmids
These are vectors made of plasmid sequences joined up by phage cos sites. Cos site represents several bases at both ends of the linear phage genome that are complementary and are able to circularize its DNA once it is inserted into the host cell (they are essentially sticky ends). The base of cosmid vectors is really small (around 4-6 kb) allowing them to accept relatively large amount of exogenous DNA (up to around 45 kb). Since they do not really have phage genes, they behave as plasmids, except that their insertion mechanism is the one from lambda phage. Basically, they are very efficient and are able to take a lot of foreign DNA, but they need more complicated procedures and their cloned sequences need further processing.
Phagemids
These hybrid vectors are based on the phages, giving them some advantages over cosmids by utilizing phage functions. Basically, they have f1 origin of replication “borrowed” from the f1 filamentous phage (it is in the same group as the phage M13). They are somewhat better because they have the ability to excise cloned DNA fragments in vivo as part of a plasmid, which removes the need for further processing of cloned sequences.
![[+]](https://www.biotechnologyforums.com/images/netpen-pro/collapse_collapsed.png)