A.
Certain RNA viruses that infect animal cells carry within the viral particle an RNA-dependent DNA polymerase called reverse transcriptase. On infection, the single-stranded RNA viral genome (~10,000 nucleotides) and the enzyme enter the host cell.
B.
The reverse transcriptase first catalyzes the synthesis of a DNA strand complementary to the viral RNA, then degrades the RNA strand of the viral RNA-DNA hybrid and replaces it with DN
C.
The resulting duplex DNA often becomes incorporated into the genome of the eukaryotic host cell.
D.
These integrated (and dormant) viral genes can be activated and transcribed, and the gene products—viral proteins and the viral RNA genome itself—are packaged as new viruses. The RNA viruses that contain reverse transcriptases are known as retroviruses.