Retroviral method
- Retroviruses are small RNA viruses that replicate through a double-stranded DNA intermediate.
- In retrovirus, RNA is reverse transcribed into DNA then it inserts a copy of its genome into the DNA of a host cell that it invades, thus changing the genome of that cell. The host cell then treats the viral DNA as a part of its own genome, transcribing and translating the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the virus. In retrovirus RNA is reverse-transcribed into DNA, which is integrated into the host cell's genome.
- It is difficult to detect the virus until it has infected the host .At that point, the infection will persist in definitely. This ability makes them well suited for certain gene therapy applications. The majority of the applications using retroviral vectors have involved ex-vivo methods in which cells are genetically modified in culture prior to introduction into the animal. However, there cent improvement in methods for production and concentration of retroviruses now allows for direct, in-vivo applications in which genes are delivered directly to the target cells.
- The retroviral approach/method has been used to express genetic embryonic tissues to allow the investigation of their developmental function.
- Retroviruses can also be used to manipulate the germ line to express genetic transgenic animals. This is done by infecting pre-implantation embryo embryonic stem cells in culture. Retroviral vectors have also been used to enhance the body's immune response to tumors. It also have been used to introduce drugs susceptibility such as herpes simplex Thymidinekinase to target cells .When we treat patients with particular drug, target cells having Tk are killed particularly.
- Advantage of retroviral vector method is of being an effective means of integrating the transgene into the genome of the recipient. These vectors can be transported in a small size (8 Kb) of DNA because of this it might lack some main constituents and can cause hindrance in the regulation. After so much of precautions during the process helper strains retroviruses could be produced by the transgenic organisms. Because of so many alternative options are available so retroviral method are hardly used for creating transgenic animals that have a commercial end use.
Structure of the integrating retroviral vector:
- The life cycle of retrovirus is different from that of Lytic viruses. Through viral enzyme reverse transcriptase the viruses infect the cells, their RNA genome and convert them to DNA. The viral DNA is inserted to the host genome when it permanently replicates along with the host DNA at each step of cell division.
- It consists of two identical single stranded RNA genomes that are each organized into 6 regions. From 5’end these regions consists of long terminal repeat(5’-LTR sequence) ; a non-coding sequence that is designated psi+ (packaging signal);three genes that can code for internal capsid;structural protein(gag);reverse transcriptase and integrate functions (pal) and an envelope protein(env);and a 3’ LTR sequence.
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| Structure of the integrating retroviral vector |
- The life cycle of retrovirus is different from that of Lytic viruses. Through viral enzyme reverse transcriptase the viruses infect the cells, their RNA genome and convert them to DNA. The viral DNA is inserted to the host genome when it permanently replicates along with the host DNA at each step of cell division.
- It consists of two identical single stranded RNA genomes that are each organized into 6 regions. From 5’end these regions consists of long terminal repeat(5’-LTR sequence) ; a non-coding sequence that is designated psi+ (packaging signal);three genes that can code for internal capsid;structural protein(gag);reverse transcriptase and integrate functions (pal) and an envelope protein(env);and a 3’ LTR sequence.
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| Retroviral Genome Strucuture |
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