7-5.
STRUCTURE
The virus is approximately 110-140 nanometers in size and has an outer
envelope surrounding the core. The core contains RNA (the genetic information),
reverse transcriptase, and a protein identified as p24. The p24 protein is antigenic, and
antibodies against it are detected in the ELISA test and Western Blot. The envelope
contains two important glycoproteins. Glycoprotein 41 (gp 41) spans the membrane
and is also antigenic. The other protein, gp 120, is the major outer membrane
glycoprotein of HIV (figure 7-1). The envelope gene that codes for a portion of the
virus's outer membrane varies considerably from isolate to isolate. An effective vaccine
for AIDS would therefore need to protect against many different strains of the virus. Human
Immunodeficiency Virus contains a gene, called the TAT (trans-activator) gene, whose product
acts as a powerful promotor of viral DNA replication. This promotion of viral replication at the
expense of cellular replication may be an important mechanism in virally induced cell
death.
Figure 7-1. Human retroviruses.
MD0838
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