Figure 1.

Components of SARS-CoV-2 and HIV. A schematic representation of SARS-CoV-2 (left) and HIV (right) is shown, along with key structural components. For both viruses, the glycoproteins, embedded within the envelope proteins are required for the initial interaction of the virus with susceptible host cells. In SARS-CoV-2, the membrane protein is required for membrane fusion and interacts with other elements of the virus. The envelope protein aids in viral assembly within the host cell, and the single-stranded RNA enclosed in the nucleocapsid comprises the genetic material. In HIV, the capsid proteins are structural proteins arranged to house the viral genetic material. Viral enzymes, coded by the pol gene, include proteases, reverse transcriptase, and integrase. The HIV reverse transcriptase is an RNA-dependent DNA polymerase essential for synthesis of viral cDNA using RNA as template. The viral integrase creates a permanent copy of viral DNA in the infected cell by catalyzing viral DNA integration into host cell DNA. The protease cleaves the newly formed polypeptide into the components of mature virions. The matrix proteins are key in virion packaging. Illustration credit: Nicholas J. Evans.