Retrovirus Resource Site

Retroviral Structure

Retrovirus particles range in size from 80–120 nm in diameter and consist of an outer envelope derived from the host cell lipid bilayer and virus encoded proteins.

The protein core of the virus consists of viral replication enzymes and the viral RNA genome. The RNA genome is truly diploid and consists of two copies of linear single-stranded (sense) RNA linked by 7–11 bp regions near the 5' termini (Billeter et al., 1974; Kung et al., 1975 and Beemon et al., 1976).

Retroviruses are divided into two categories based on the complexity of their genomes, simple and complex. RNA from simple retroviruses consists of three major coding domains; gag which includes the proteins making up the matrix, the capsid and the nucleoproteins; pol, which encodes the reverse transcriptase and integrase and env, which codes for the proteins making up the viral envelope. An additional smaller coding domain, pro encodes the viral protease. Simple retroviruses include most oncogenic viruses, for example Moloney Murine Leukemia Virus (MMLV) (Moloney, 1960) and Mouse Mammary Tumor Virus (MMTV) (Bittner, 1936).

Complex retroviruses have regulatory domains in addition to gag, pol and env; for example, the trans-activating factors, tat and rev from HIV-1. This group of viruses consists of the lentiviruses including Human Immunodeficiency Virus (HIV-1) (Barre-Sinoussi, et al., 1983; Gallo, et al., 1984, Levy, et al., 1984 and Letvin, et al.,1985) and the spumaviruses, Human Foamy Virus (HFV; Achong, et al., 1971) and Simian Foamy Virus, SFV (Enders & Peebles,1954; Rustigian, et al., 1955).

Figure 1. Wild type retrovirus life cycle.