Genomic HIV-RNA duplex, molecular model. This structure shows the dimerization initiation site of genomic HIV-1 with RNA (ribonucleic acid), which has been shown to be an extended duplex with two adenine bulges. HIV (human immunodeficiency virus) causes AIDS (acquired immunodeficiency syndrome). It is a retrovirus, an RNA virus that incorporates itself into the host genetic material, prompting it to produce new copies of the virus. The structure shown here is an important step in retroviral replication. There are two strands (pink and green) forming the double helix shape.