Genome The genome of the gammaretrovirus is a single-stranded RNA (+) genome that is approximately 8.3 kb in size. It has a 5’ cap with a 3’ poly-A tail, and it contains two long terminal repeater regions at both the 5’ and 3’ ends. These long terminal repeat regions have the U5, R, and U3 regions as well as a polypurine tract at the 3’ end and a primer binding site at the 5’ end. The typical gammretrovirus genome contains the gag gene, pol gene, and an env gene. Replication cycle The gammaretrovirus will act as a parasite to use cellular host factors to deliver genome into a host's cell nucleus, where they will use the cell's machinery to replicate the viral genome and continue the spread throughout the host organism. Because it is a single-stranded RNA(+) with a DNA intermediate genome, it has the ability to copy its viral RNA genome directly into mRNA. Against the central dogma of biology, it also reversely transcribes its RNA genome into DNA. Virion attach the host cell receptors via the SU glycoprotein, then the TM glycoprotein assists with fusion with the cell membrane. The virus will then begin uncoating, and a linear double-stranded DNA molecule is formed from the single-stranded RNA(+) genome via reverse transcription. The enzyme responsible for reverse transcription is reverse transcriptase. The host nuclear membrane is disassembled during mitosis and the viral double-stranded DNA is able to enter the host nucleus. Viral double-stranded DNA is then integrated into the host cell genome via viral integrase, an enzyme that allows for viral DNA integration into host DNA. The virus is now referred to as a provirus, which means the gammaretrovirus DNA has integrated into the host cell genome and is now the template for the formation of viral mRNA and genomic RNA. Double-stranded DNA is transcribed by Pol II and will produce both spliced and unspliced RNA strands, these spliced RNA strands will leave the host cell nucleus. The unspliced viral RNA translation produces env, gag, and gag-pol polyproteins. The Env becomes a polypeptide precursor and will cleave to produce a receptor binding surface. Next the virion is assembled in the host cell membrane, and the viral RNA genome is packaged. The virions bud from the plasma membrane and release into the host. After virions release from host cells the process is repeated on the next cell the active viral