The formation of a provirus begins when a virus infects a host cell. Specifically, retroviruses carry an enzyme called reverse transcriptase that converts viral RNA into DNA. This viral DNA is then transported into the nucleus of the host cell, where it is integrated into the host's genome through the action of another enzyme known as integrase. Once integrated, the viral DNA is termed a provirus, and it can be transcribed and translated using the host's cellular machinery.
