Gammaretrovirus

Gammaretrovirus is a genus of the Retroviridae family, within the subfamily Orthoretrovirinae. Exogenous gammaretroviruses infect a variety of mammals and are characterized by a single-stranded positive-sense RNA genome of about 8 to 10 kilobases that encodes gag, pol, and env genes, flanked by long terminal repeats. Like other retroviruses, they reverse-transcribe their RNA into DNA and integrate it into the host genome as a provirus.

Replication follows the standard retroviral lifecycle. The virus attaches to a host cell, releases its core, and reverse transcription converts RNA into double-stranded DNA. The pre-integration complex enters the nucleus and integrates into host DNA, after which viral transcripts are produced and translated into structural and enzymatic proteins. Virions assemble at the cytoplasmic membrane and bud with an envelope derived from the host cell. Integration is typically linked to activated or dividing cells in many gammaretroviruses.

Major members include murine leukemia virus (MuLV) and feline leukemia virus (FeLV); other examples are gibbon ape leukemia virus (GALV) and spleen necrosis virus (SNV). The genus comprises both exogenous pathogens and endogenous retroviral sequences embedded in host genomes. Host range is generally species-specific, though cross-species transmissions and endogenization have occurred in evolutionary history.

Disease associations vary by virus and host. In mice, MuLV can induce leukemia or lymphoma; FeLV in cats is associated with immunosuppression, anemia, and lymphoma. Oncogenesis often involves insertional mutagenesis rather than oncogene expression by the virus itself. Transmission occurs mainly through close contact, saliva, bodily fluids, or milk, with vertical transmission in some species.

Gammaretroviruses have played a significant role in biotechnology as gene therapy vectors, but concerns about insertional mutagenesis have driven ongoing improvements and safety considerations. Endogenous gammaretroviral sequences are widespread in some species and contribute to genome evolution.