To complement the answer: the two HIV RNA strands can also be genotypically different, which occur when a cell is infected by two distinct HIV strains. Subsequently, reverse transcriptase in a newly infected cell can then jump from one RNA strand to the other and generate a new mosaic recombinant with "patches" of the two original strands. This recombination process provides a tremendous advantage for HIV to escape from host pressures in a single round of infection. Such smart virus!

The 2 strands of HIV RNA are identical, and are dimerized with other, which is very characteristic of Retroviruses. Apparently both are required for a successful viral replication. This publication will make you understand why, since it is a really complicated process and this article does a great job at explaining it.

http://www.ncbi.nlm.nih.gov/pubmed/19529749

Hi, Dr. Mahdi, thank you very much for your help. I am reading the paper you refer me.;) It did help me a lot to understand the question.

To complement the answer: the two HIV RNA strands can also be genotypically different, which occur when a cell is infected by two distinct HIV strains. Subsequently, reverse transcriptase in a newly infected cell can then jump from one RNA strand to the other and generate a new mosaic recombinant with "patches" of the two original strands. This recombination process provides a tremendous advantage for HIV to escape from host pressures in a single round of infection. Such smart virus!

The proposed reasons are:

1)    VERY IMPORTANT POINT: It has also been proposed that the ability of the virus to package two RNA molecules and to switch RNA templates during reverse transcription allows frequent recombination in order to increase genetic diversity. When two viruses with different genotypes infect the same cell and produce heterozygous virions, there is the potential for recombination between them to result in a mixing of the genetic materials and the creation of a new hybrid genotype. In essence, this allows the virus to replicate sexually. So, two RNA molecules proves a lot of diversity in the retrovirus for which it’s very difficult to completely cure a patient (such as AIDS patient) of Retrovirus infection (such as HIV-1 infection) by common anti retroviral therapy.

2)     It has been postulated that viral RNA is sometimes damaged prior to the initiation of reverse transcription. Packaging two copies of the viral genome would allow the reverse transcriptase complex to switch templates when encountering a break in the viral RNA, and thereby complete DNA synthesis and rescue the genetic information, despite the damage to the RNA genome. This is the basis of the copy-choice model of retroviral recombination.

3)     These two RNA molecules often form dimer. The dimerization of genomic RNA appears to be essential for successful replication of Retroviruses such as HIV-1.

Reference:

HIV-1 RNA Dimerization: It Takes Two to Tango Michael D. Moore and Wei-Shau Hu HIV Drug Resistance Program, National Cancer Institute, Frederick, MD, USA AIDS Rev. 2009 ; 11(2): 91–102.

http://www.ncbi.nlm.nih.gov/pubmed/19529749