Viral vectors  

There are a large number of viral vectors available which can transfer the desired sequence properly into the host. Examples of the viral vectors are as follows:

• Adenoviral vectors:  They are most widely used vectors which are capable or transferring large DNA inserts (up to 35 kilo base pairs). Adenoviruses are human viruses and hence can transduce a large number of human cells efficiently. They have been used in diseases like cystic fibrosis (Anderson, N.D). Their capacity to infect quiescent and dividing cells and producing high-titre viral stocks has increased their application (Gould and Favorov, 2003).

• Adeno-associated viral vectors: This non pathogenic mammalian virus shows a high prevalence within human beings. It specifically integrates into the short arm of the human chromosome and does not produce diseases (Anderson, N.D). As the genome of AV is small it allows the transfer of about 4.8 kb of DNA. This vector has been used during the experimental studies of diabetes and arthritis.

• Herpes simplex virus: A large part of the long genome of HSV (150 kb) can be replaced with a foreign DNA. This does not effect the viral growth and allows the transfection of multiple genes. They have the capacity to transduce nervous cells and other cell types also. The infection of cells by HSV is a complex process which involves the interaction between viral glycoproteins and proteoglycans of the host cell surface (Gould and Favorov, 2003).

• Retroviral vectors: The retroviral genome is linear stretch of RNA which is 7-11 kb long. General components of the retroviral genome are two LTRs, located at the terminal positions of the genome and cis-signals lie adjacent to LTRs. These cis-signals are responsible for integration and reverse transcription. These regions are utilized during the designing of the retroviral vectors (Gould and Favorov, 2003).