Final answer:
Retroviruses, such as HIV, can acquire cellular genes by reverse transcribing their RNA genome into DNA and incorporating it into the host cell genome. This process requires the virus-specific enzyme reverse transcriptase, which is not found in uninfected host cells. Researchers have developed drugs that specifically target these viral enzymes without affecting the host's metabolism.
Step-by-step explanation:
Retroviruses, such as HIV, have an RNA genome that must be reverse-transcribed into DNA, which then is incorporated into the host cell genome. To convert RNA into DNA, retroviruses must contain genes that encode the virus-specific enzyme reverse transcriptase that transcribes an RNA template to DNA.
Reverse transcription never occurs in uninfected host cells—the enzyme reverse transcriptase is only derived from the expression of viral genes within the infected host cells. The fact that HIV produces some of its own enzymes not found in the host has allowed researchers to develop drugs that inhibit these enzymes without affecting the host's metabolism.