So remember, HIV is that viral agent that causes AIDS in humans. So all living organisms basically produce RNA from DNA. So in our body, for example, we take DNA then we transcribe it into RNA and then the RNA is used to synthesize a variety of different types of proteins. But the special thing about these retroviruses is and that's actually where they obtain their name they are able to actually synthesize viral DNA molecules from RNA and that is in reverse of what happens in our own cells and all other living cells. So, however, a category of viruses called retroviruses can synthesize DNA from RNA by using a special type of protein that is found in that retrovirus known as reverse transcriptase. And so one example is the HIV agent.