Retrovirus Life Cycles

Reverse transcriptase is an enzyme that synthesizes complementary DNA from the retrovirus's single-stranded RNA genome after the virus enters the host cell. Over time, this enzyme creates double-stranded DNA, reversing the usual pattern of DNA-to-RNA transcription. This DNA copy is then integrated into the host genome, allowing the retrovirus to replicate whenever the host's DNA is transcribed.

Once integrated into the host genome, the retroviral DNA forms a provirus and is actively transcribed whenever the host DNA is transcribed. This produces messenger RNA that exits the nucleus and enters the cytoplasm, where it is translated into new viral proteins. These proteins assemble into new retroviruses that bud from the cell, ready to infect other cells.

HIV's single-stranded RNA genome accumulates mutations rapidly, allowing the virus to evolve resistance to any single drug quickly. Antiretroviral cocktails (HAART) target multiple stages of the retroviral life cycle simultaneously, making it statistically unlikely that the virus will develop resistance to all drugs at once. Understanding viral mutations and hiv evolution is key to this strategy's success.

Fusion inhibitors are antiretroviral drugs that block the retrovirus from entering the host cell by preventing the fusion of the viral membrane with the host cell membrane. By inhibiting this initial fusion step, these drugs prevent the virus from delivering its genetic material into the cell, stopping infection before replication can begin.

Integrase is an enzyme that integrates the retroviral DNA into the host cell's genome inside the nucleus. This integration creates a provirus, embedding the viral genetic material into the host DNA so that it is transcribed along with normal host genes. Integrase inhibitors are antiretroviral drugs designed to prevent this critical integration step.

Reverse transcriptase inhibitors are competitive inhibitors that incorporate themselves into the growing DNA strand during reverse transcription instead of normal DNA bases. Once incorporated, these drug molecules block further progress by the reverse transcriptase enzyme, preventing the synthesis of double-stranded DNA needed for viral integration and replication.

Protease inhibitors interfere with the enzymatic reactions necessary for producing fully functioning retroviral particles. By disrupting protease activity, these drugs prevent the proper assembly and maturation of new retroviruses, rendering newly formed viral particles unable to infect other cells effectively.