Vector (genetic engineering)
In genetic engineering and biotechnology , a vector is understood to be a transport vehicle (“gene ferry”) for the transfer of a foreign nucleic acid (often DNA ) into a living recipient cell by transfection or transduction .
Various such vehicles are called vectors:
- Plasmids which, for example, make it possible to clone a specific section of DNA,
- Cosmids or YACs that can transfer large sections of DNA with the help of bacteriophage or yeast cell structures ,
- and modified viruses (e.g. adenoviruses or retroviruses ), also known as viral vectors .
Vectors are divided into cloning vectors and expression vectors according to their use .
Suitability of a vector
Different vectors may have different suitability as transport vehicles depending on the given framework conditions. The vector should be able to be smuggled into the recipient cell as simply as possible (the specific immune defense , among other things, plays a role here) and it should be able to replicate independently of its main genome in order to ensure strong reproduction.
| vector | Max. Capacity ( kbp ) | reason |
|---|---|---|
| Plasmid | 10-15 kbp | otherwise no ring formation |
| M13 phage | <6 kbp | otherwise no packaging |
| Phagemid | <6 kbp | otherwise no packaging |
| λ phage | <25 kbp | otherwise no packaging |
| Cosmid | <50 kbp | otherwise no packaging |
| P1 phage | 30-100 kbp | ? |
| BAC | 100-300 kbp | ? |
| PAC | 100-300 kbp | ? |
| YAC | 20-2000 kbp | Instability in mitosis and meiosis |
Vector types
Vectors are divided into different types according to the creatures they carry. Each type has certain properties and thus says something about the suitability of the vector. After a transgene has been inserted by cloning , the vector is also colloquially referred to as a construct . The specific adaptation of a vector is known as vector design .
Plasmid vectors
Plasmid vectors are vectors that are obtained from plasmids . Often prokaryotes carry plasmids, but also some eukaryotes (yeast cells). The most widely used host cell for plasmid vectors is the bacterium Escherichia coli . This bacterium is probably one of the most frequently used organisms in genetic engineering.
The advantages of plasmid vectors are clear: they are easy to use because they are small, and they can easily be obtained in larger quantities from cells by plasmid preparation . In addition, plasmids are not essential for cell survival. An intervention therefore seldom affects the host cell. In addition, plasmids are replicated independently of the bacterial chromosome and can therefore exist in many copies in the cells. The number of copies depends on the nature of the plasmid and the origin of replication (origin of replication). The main disadvantage of plasmid vectors is their low capacity: even with a DNA fragment of 5 kb in length, the effectiveness of the cloning decreases. The maximum possible length is 10–15 kb. Since longer sequences are cloned in many cases, other vectors are required.
Viral vectors
Modified viruses that transduce eukaryotic cells and, in doing so, can smuggle foreign genes into these cells are called viral vectors . They are used, for example, in gene therapy .
Bacteriophage vectors
Bacteriophages (“phages” for short) are viruses that attack bacteria. They are divided into different groups according to their host cell.
The use of bacteriophage vectors is based on the phage lysogenic cycle . Viruses can be divided into virulent and temperate. Virulent viruses have a lytic cycle , which means that they invade their host cells and cause them to form new viruses. Temperate viruses have a lysogenic cycle, they build their genome into that of the host cell.
This is what researchers are interested in. By incorporating the virus genome, a DNA fragment to be examined can also be introduced into the cell.
Cosmids
So-called cosmids are obtained by incorporating cos-sites from λ phages into plasmids . Its genome has short, single-stranded ends that are complementary to each other and can thus close to form a ring. These ends are called the cos region (cohesive sites: cohesive ends).
The great advantage of cosmids in contrast to plasmid vectors is that they themselves are much shorter and therefore have a greater absorption capacity. Cosmids can accommodate sections up to about 47 kb in length and thus even surpass phage vectors.
Cosmids are processed like bacteriophage vectors. However, since they do not contain phage genes, they behave like plasmids in the host cell. This makes them very attractive vectors. However, cosmids are difficult to handle, which offsets the benefits.
Phagemids
A phagemid (sometimes also a phasmid ) is a plasmid which carries an origin of replication for the single-stranded replication of f1 phages. So it is also a hybrid of plasmid and phage. If the phagemid is present in the cell in the form of a plasmid, the genes on it can be expressed .
Germ cells
Sperm -mediated gene transfer uses sperm to insert DNA into egg cells as part of artificial insemination .
See also
literature
- DST Nicholl: Genetic Engineering Methods ( ISBN 3-86025-298-4 ; 178 pages) Introduction to general areas of genetic engineering.