So there are many examples of viruses in nature that follow this same pathway that is followed by the tobacco mosaic virus. That is, they form RNA agents or RNA molecules from other RNA molecules. Now, another interesting category of viruses are the retroviruses and one example of a retrovirus is HIV. 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.