In [Wilk et al. 2001][1] I saw that HIV has 3 open reading frames. In the [Watts et al. 2009][2], I noticed they mentioned HIV has 9 open reading frames. I don't understand this very well. 

e.g. 

1. `[ATG] GAT GTA AGT`
2. `A[TG G]AT GTA AGT`
3. `AT[G GA]T GTA AGT`

Could anyone explain this to me?


  [1]: http://jvi.asm.org/content/75/2/759.full
  [2]: http://www.nature.com/nature/journal/v460/n7256/full/nature08237.html