Vector (molecular biology)

In genetic engineering and biotechnology is meant by a vector a transport vehicle ( "gene ferry " ) for the transmission of a foreign nucleic acid (often DNA) into a living recipient cell by transfection or transduction.

As vectors, several such vehicles are called:

• Plasmids, for example, allow the cloning of a specific DNA segment,
• Cosmids or YACs, which can be transferred by means of bacteriophages or Hefezellstrukturen large DNA sections,
• And modified viruses (e.g., adenovirus or retrovirus ) which are also referred to as viral vectors.

Suitability of a vector

Different vectors may have different suitability as transport vehicles in accordance with the circumstances. The vector should be as simple as possible to inject into the recipient cell can ( plays among other things, the specific immune defense, a role ) and he should be able to replicate independently of the main genome in order to ensure a strong increase.

Vector types

Vectors are classified into different types according to the creatures that they carry. Each type has certain properties and thus says something about the suitability of the vector from. After insertion of a transgene by cloning the vector is also colloquially referred to as a construct. The specific adaptation of a vector is called the vector design.

Plasmid vectors

Plasmid vectors are vectors that are derived from plasmids. Frequently prokaryotes carry plasmids, but also some eukaryotes ( yeast cells ). The host cell is most widely used plasmid vectors, the bacterium is Escherichia coli. This bacterium is probably one of the organisms in genetic engineering most commonly used.

The advantages of plasmid vectors are clear: they are easy to use because they are small and can be easily recovered by a plasmid in larger quantities from cells. In addition, plasmids are not essential for cell survival. An intervention rarely has therefore an impact on the host cell. Moreover, the plasmids are replicated independently of the bacterial chromosome and can therefore exist in the cells in multiple copies. Here, the number of copies depending on the nature of the plasmid and the replication of the starting point ( origin of replication ). The main disadvantage of plasmid vectors is their low capacity: Even with a DNA fragment of 5 kb in length decreases the efficiency of cloning. The maximum length is 10-15 kb. Since in many cases, longer sequences are cloned, one has to rely on other vectors.

Viral vectors

As viral vectors modified viruses are referred to transduce eukaryotic cells, and it can inject foreign genes into these cells. They are used for example in gene therapy.

Bacteriophage

Bacteriophages (in short: " phages " ) are viruses that infect bacteria. They are divided into different groups according to their host cell.

The use of bacteriophage is based on the lysogenic cycle of phages. Viruses can be divided into virulent and temperate pension. Virulent viruses have a lytic cycle, that is, they penetrate into their host cell and cause it to form new viruses. Tempe pension viruses have a lysogenic cycle, they build their genome into the host cell.

Therein lies the interest of researchers. By the incorporation of the virus genome to be examined, a DNA fragment may be introduced into the cell.

Cosmids

Through the incorporation of cos -sites from λ phage into plasmids obtained so-called cosmids. Its genome has short single-stranded ends that are complementary to each other, allowing them to connect to a ring. These ends are as cos region (English cohesive sites: cohesive ends ) called.

The great advantage of cosmids in contrast to plasmid vectors is that they are much shorter, and therefore have a greater recording capacity. Cosmids can accommodate up sections about 47 kb in length and even exceed by phage vectors.

Cosmids are processed as bacteriophage. However, since they contain no phage genes, they behave in the host cell, such as plasmids. This makes them very attractive vectors. However, cosmids are difficult to handle, so the benefits are balanced again.

Phagemids

Phagemid (sometimes called " phasmids ") is a plasmid containing a origin of replication contributes to single-stranded replication, F1 phage. Thus, it is also a hybrid vectors from plasmid and phage. If the phagemid in the form of a plasmid in the cell, so the genes lying on it can be expressed.

Germ cells

Sperm -mediated gene transfer, sperm used to introduce into oocytes in the context of in vitro fertilization DNA.