The 3D retrovirus is unique to other viruses in that it carries its genomic information in RNA, not the standard DNA that most do.
The retrovirus is somewhat of an oddity in the world of molecular biology. It's name is indicative of why this molecule stands out from other viruses. Most viruses take over their host cells by injecting them with their own viral DNA, which then follows the central dogma of molecular biology to transcribe RNA and translate proteins. What the retrovirus does, however, is inject its own viral RNA into the cell which then encodes the viral DNA to be produced within the host cell. This goes retroactively to the traditional order of DNA to RNA to proteins, hence the name, retrovirus. The retrovirus itself stores its genome on two strands of RNA that eventually injected into the cytosol of the host cell along with enzymes such as reverse transcriptase that initiate the reversed transcription of DNA from the viral RNA. This newly formed DNA is integrated into the genome of the host cell, and is now referred to as a provirus. This reversed transcription lacks "proof-reading" mechanisms otherwise had, and consequently mutations occur frequently in a typical retrovirus. It is for this reason, vaccines against retroviruses-such as HIV-are so difficult to obtain.
Not all retroviruses are bad as it may seem. Some insert into human DNA and are passed on to succeeding generations, becoming endogenous retroviruses. These endgenous retrovirus play an important role in protecting the genome against some infections of other harmful retroviruses and even assisting in development during gestation.