Structure and properties of HIV

1. Shape and size

• HIV is a spherical virus of about 90 nm in diameter.
• Size; 90nm

2. Envelope:

• HIV is enveloped virus. The envelope is a lipid bilayer surrounding the viral matrix, which is derived from host cell membrane during budding.
• Below the envelope, there is an icosahedral shell called matrix (P17).

3. Core:

• The core consists of cylindrical capsid (P24) which surrounds the genome.

4. Genome:

• HIV is ss RNA virus. The genome consists of two identical copies of +SS RNA and protein which are linked at their 5’ end.
• Genome of HIV consists of 9 gene, 3 structural gene and 6 non-structural gene (regulatory gene).
• Structural gene (env,gag and pol), regulatory gene (tat,rev,nef,vif,vpr and vpu in HIV-I and vpx in HIV-2)

5. Enzymes:

• Reverse transcriptase (RNA dependent DNA polymerase)
• Protease
• Intrigase
• Ligase

6. Replication:

• Cell specific (CD+T cell)
• Virus entry: receptor mediated (gp120 and gp41)
• RNA Replicates to form DNA intermediate by Reverse transcriptase enzyme
• Provirus remains permanently associated with host cell
• Release; budding

7. Other properties:

• Oncogenic
• Mutation
• Species specific
• Family: Retroviridae

HIV genome and proteins

• HIV has two identical copies of +SS RNA genome. The genome consists of 3 structural gene and 6 regulatory gene.
• Structural gene; env, gag and pol gene
• Regulatory gene; tat, rev, nef, vif, vpr and vpu in HIV-I and vpx in HIV-2)

1. Structural gene:

i. Gag gene:

• Gag gene encodes the precursor protein P55 which is cleaved by viral protease (P10) to form matrix protein (P17), Capsid protein (P24) and Nuncleocapsod protein (P7 & P9). Gag gene helps to form core of virus.

ii. Pol gene:

• Pol gene encodes the precursor protein P100 which is cleaved to form Protease (P10), reverse transcriptase and endonuclease.

iii. Env gene:

• Env gene encodes the precursor protein gp160 which is cleaved to form surface spike glycoprotein (gp120) and transmembrane protein (gp41).
• Genetic variety of HIV strain resides in env

2. Regulatory gene:

i. Tat gene: ( transactivator of transcription)

• It encodes transactivator protein (P14) which promotes the transcription of viral genome.

ii. Rev gene: (regulatory of expression of viral protein)

• It encodes Rev protein (P19) and promotes the expression of viral structural proteins

iii. Nef gene: ( Negative expression factors)

• It encodes precursors protein P27
• It down regulates the expression of CD4 cells, macrophage and MHC-II.

iv. Vif gene: (Virion infectivity factor)

• It encodes the precursor protein p23 and promotes the viral infectivity by suppression the inhibitory actions of host cell proteins.

v. Vpr gene:

• It encodes the precursor protein P15.
• It promotes the transport of viral pre-initiation complex into nucleus of host cell.

vi. Vpu gene in HIV-I / Vpx gene in HIV-II

• It encodes the precursor protein P16.
• It promotes maturity and releases of progeny virus from host cell.

Structure, genome and proteins of HIV

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