7-6. HUMAN IMMUNODEFICIENCY VIRUS REPLICATION AND TRANSMISSION
The HIV contains a unique enzyme that enables the viruses to make DNA copies of
its RNA. This enzyme, commonly referred to as reverse transcriptase, is an
RNA-dependent DNA polymerase that catalyzes the reverse flow of genetic information
from RNA to DNA. Once the DNA is made, these viruses use other enzymes to insert
or integrate the DNA copies of their genes into the chromosomal DNA of the host cell.
Insertion having been accomplished, the proviral DNA genes become a part of the
genes of the host cell. Once present in the cellular DNA, retrovirus "proviral" genes
may be: (1) nonfunctional or silent, (2) partially transcribed with subsequent expression
of individual viral proteins within the cell or on its surface, or (3) fully transcribed to
produce new viral RNA genes that are encapsulated in viral structural proteins to form
new virus particles, which subsequently "bud" from the surface of the host cell. These
new virons may then infect any cell they contact (figure 7-2).
Binding of viruse to target cell.
Uncoating of virus and transcription of viral RNA to DNa by reverse transcriptase.
Transcription and protein synthesis.
Assembly of viral proteins and RNA at cell surface.
Budding of mature viral particle from host.
Figure 7-2. Life cycle of retroviruses.