Retroviruses are a part of Retroviridae, a family of viruses. Retroviruses are considered to be class IV viruses and contain double stranded RNA genomes. They contain ribonucleic acid (RNA), a genetic material. Retroviruses reverse the normal cell process, where RNA is used to synthesize DNA.
Certain types of cancers and a range of viral infections can occur in both humans and animals. These infections and types of cancers come from retroviruses. An example of this is the virus Acquired Immune Deficiency Syndrome (AIDS), which is caused by the Human Immunodeficiency Virus (HIV).
So which enzymes do retroviruses contain? There are three enzymes in viruses: viral protease (PR), reverse transcriptase (RT), and integrase (IN). The enzymes make it possible for retrovirus’ RNA to perform as a template of sorts for the transcription process.
The reverse transcriptase (RT) enzyme is responsible for the conversion of the single stranded genomic RNA into double stranded proviral DNA. The enzyme can both copy minus strand DNA from genomic RNA and catalyze the synthesis of a complementary plus DNA strand. The resulting double stranded DNA is integrated in the host chromosomes and is transcribed by the host’s own machinery. The resulting transcripts are either used to synthesize proteins or produce new viral particles. These new viruses are released by budding, usually without killing the host cell.
Viral protease (PR) is the enzyme that converts the immature virion into a mature virus through the cleavage of precursor polypeptides. It specifically recognizes and breaks apart a given protein or similar proteins. The destruction of the proteins is accomplished by the ability of the protease to break the peptide bonds that the link the constituent parts of the protein- the amino acids- together.
A protease is present in every living cell of every living organism. As soon as the cells are disrupted, the protease are released and can quickly degrade any given protein of interest. This is highly undesirable, as the protease destruction of other proteins greatly reduces the yield of the target protein in isolation.
Chemical substances called protease inhibitors can prevent viral protease activity. Protease inhibitors include any substance that partially or completely blocks the functioning of the protease. To combat HIV, for example,, protease inhibitors are usually administered as a cocktail with other agents that block the transcription of the viral RNA into DNA. Monitoring of the body’s response is important, as resistance to protease inhibitors can develop.
The enzyme, integrase (IN) inserts the proviral DNA into the host cell genome. It enables its genetic material to be integrated into the DNA of the infected cell.
Integrase inhibitors are oligonucleotides. The inhibitors are small segments of DNA or RNA which are synthetically prepared. Modified oligonucleotides can serve to block RNA/DNA interactions and modify protein or enzyme synthesis. The drawback of the inhibitor is that it has only one chance to act for each cell.
Annual Reviews. “The Retroviral Enzymes,” https://mbb.rutgers.edu/411files/AG/Katz-1994.pdf
New England Biolabs. “M-MuLV Reverse Transcriptase,” https://www.neb.com/nebecomm/products/productM0253.asp