Retroviruses are RNA-containing viruses that use the enzyme reverse transcriptase to copy their RNA into the DNA of a host cell. Retroviruses have been isolated from a variety of vertebrate species, including humans, other mammals, reptiles, and fish. The family Retroviridae includes such important human pathogens as human immunodeficiency virus (HIV) and human Tlymphotropic virus (HTLV), the causes of AIDS and adult T-cell leukemia respectively. The study of this virus family has led to the discovery of oncogenes, resulting in a quantum advance in the field of cancer genetics. Retro-viruses are also valuable research tools in molecular biology and gene therapy.

Characteristics

The classification of retroviruses is based on comparisons of the size of the genome and morphologic characteristics (see Table 1). The genomic RNA