Structure, genome and proteins of HIV
Structure and properties of HIV
- Shape and size
- HIV is a spherical virus of about 90 nm in diameter.
- Size; 90nm
- 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).
- The core consists of cylindrical capsid (P24) which surrounds the 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)
- Reverse transcriptase (RNA dependent DNA polymerase)
- 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
- Other properties:
- 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.