Overview

A retrovirus is a type of virus whose genome is composed of RNA and whose replication cycle includes an obligatory step of copying its RNA into DNA. That DNA copy can be inserted into the host cell's genome, allowing the viral genetic information to persist and be expressed as part of the cell's own DNA. Retroviruses influence evolution, can cause disease in animals and humans, and are used as tools in molecular biology.

Structure and genetic components

Typical retroviruses belong to the family Retroviridae and carry a small set of genes that commonly include gag (structural proteins), pol (enzymes such as reverse transcriptase, integrase and protease), and env (envelope proteins). They package their RNA genome inside a protein capsid and enclose that core within a lipid envelope studded with viral glycoproteins.

Replication cycle

The replication cycle distinguishes retroviruses from many other viruses. Major steps include:

  1. Entry into a susceptible cell by fusion or endocytosis mediated by envelope proteins.
  2. Release of the RNA genome and associated enzymes into the cytoplasm.
  3. Reverse transcription: copying viral RNA back into complementary DNA by reverse transcriptase.
  4. Integration of the newly formed viral DNA into the host genome by integrase, creating a provirus.
  5. Transcription and translation of viral genes using host machinery, assembly of new particles, and release to infect other cells.

Variability, clinical significance and treatment

Reverse transcriptase lacks the proofreading fidelity of many cellular DNA polymerases, so errors introduced during RNA-to-DNA conversion lead to a high mutation rate. This genetic variability can enable rapid evolution under selective pressures such as antiviral drugs or immune responses. Human immunodeficiency virus (HIV) is the most prominent human retrovirus and illustrates how mutation and integration complicate therapy and vaccine development. Modern treatments combine drugs that target reverse transcriptase, integrase and viral protease to suppress replication and reduce the chance of resistance.

History, types and research uses

Reverse transcriptase was discovered in 1970, changing fundamental ideas about genetic information flow. Retroviruses include several genera (for example lentiviruses, which include HIV) and some can become endogenous elements when proviral DNA is inherited across generations. Engineered retroviral vectors are widely used in gene delivery and research, although their propensity to integrate into host genomes requires careful safety evaluation to avoid insertional mutagenesis.

Further information

For general definitions and introductory material see virus, for discussion of host genome integration see DNA, for mechanisms of reverse transcription see reverse transcription and for basic RNA concepts see RNA. Research, clinical practice and public resources continue to expand understanding of these versatile and medically important agents.