viral vector - retroviral vectors (Jan/08/2010 )

Dear all,

I have been reading some information on retroviral vectors, but I have a question on a statement made in the notes I got.

The author states that the env, pol and gag genes are removed from the retrovirus and that the transgenes are replacing those genes.


However when the env, pol and gag genes are gone, then how can the virus still infect his host?
(ex.: pol genes, the virus needs this for the reverse transcriptase...)


Or does the author mean that when those genes are deleted to insert the transgene you need to use a second helper virus that still has those genes to help infect the host ?

Or?

The genes are removed from the actual plasmid but when you want to make these viruses, these genes are supplied as additional helper plasmids ( Triple plasmid trasnfection is used for virus preps).