Most commonly used retroviral vector is Monkey murine    leukaemia virus vector system which is used to treat ADA-SCID.  

A recombinant retro virus vector genome that is packaged  in the envelope protein of another virus will have the  binding specificity and infection spectrum that are  determined by the envelope protein called pseudo type formation.   

The viral genes “gag”, “pol” and “env” are present in  retroviruses and these genes are responsible for genomic and protein assembly.

These vectors have potential for permanent expression in somatic cell.  

After transfection, the ssRNA is reverse transcribed into double stranded DNA, by which the inserted genes gets integrated into host genome and translated into proteins.   

The retrovirus genome is approximately 10 kb and  contains three genes: 

Each end of the genome has long terminal repeats (LTRs)  which has the promoter/enhancer regions. 

Some retroviruses contain proto-oncogenes which when mutated can cause cancers, during packaging of vectors, these oncogenes are removed.  

The retroviral vectors are manipulated to increase the yield of virus particles, increase the efficiency of transduction, engineering them to infect non-dividing cells and specifying cell type.