Practice question

Retroviruses such as HIV, MLV and HTLV store genetic information as two copies of positive-sense single-stranded RNA genome of 7-12 kb containing gag, pol and env genes flanked by long terminal repeats. Positive-sense denotes same polarity as mRNA, translatable although retroviruses first reverse transcribe RNA into double-stranded DNA provirus using virion reverse transcriptase. Diploid RNA allows recombination during reverse transcription, enhancing diversity. Packaging two RNAs ensures repair of breaks and promotes strand switching. Genome organization distinguishes them from negative- and double-stranded RNA viruses.