In the older literature I saw that HIV has 3 open reading frames. In the newer paper, however, I noticed it 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?