Yup, that's the "common" characteristics of retroviruses....why I call it common??because there're three subfamilies of retroviruses: Oncovirus, Lentivirus and .....virus..(argh, I forgot the name)..poor me..
Why it does so? because according to Baltimore virus' classification, retroviridae is classified into dsRNA with DNA intermediate (reverse transcriptase) which has a diploid RNA attached to reverse transcriptase enzyme for each of them....and also, in order to do capsid "uncoating", they have to do so..
gag is a code for virion's protein construction.
gp = glycoprotein...
so, gp120 = glycoprotein code 120...
easy isn't it..
don't say like that Nite, because I'm also a newbie in Virology and now, I'm learning for the next virus which is Herpesvirus..