Final answer:
Retroviruses use reverse transcriptase to create DNA from RNA, transcribe this DNA into mRNA to produce proteins, and sometimes bypass the DNA stage using RNA-dependent RNA polymerase to directly create mRNA.
Step-by-step explanation:
Retroviruses, such as HIV, employ several mechanisms to create different proteins. Firstly, retroviruses use reverse transcriptase to convert their RNA genome into DNA, which is then integrated into the host cell's genome.
Secondly, the integrated viral DNA is transcribed into messenger RNA (mRNA), which is translated into proteins necessary for the virus to replicate. Finally, in some cases, retroviruses may use their viral genes to encode RNA-dependent RNA polymerase to produce mRNA directly from the RNA genome, bypassing the DNA stage altogether.