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31.1 General Concept

 

a.  Out of three subfamilies of Retroviruses two infect humans namely oncornaviruses (Human T Cell Lymphotrophic Viruses (HTLV) I, II, and V) and lentiviruses (HIV 1, HIV 2).

HTLV-I causes cutaneous T-cell lymphomas,

HTLV-II causes hairy T-cell leukemias,

HTLV-V causes T-cell lymphomas and leukemias.

HIV-1 causes Acquired Immunodeficiency Syndrome (AIDS),

HIV-2 causes AIDS related syndrome in Africa.

b. Retroviruses contain RNA genome and an enzyme called reverse transcriptase, which makes circular DNA by using RNA as a template. The viral DNA integrates with the host cell chromosomes.

c.  HIV is an enveloped virus which contains glycoprotein 120 (gp120) which binds to CD4 receptor present over the T helper cell.

d.  Genome of HIV composed of two positive strands RNA which are capped at 5'end and polyadenylated at 3'end.

e.  The tRNA acts as a primer for the synthesis of DNA using RNA as a template.

f.  Long terminal repeats (LTR) present towards both the ends help in the integration of viral genome to host genome. It also serves as promoter and enhancer for the viral genome.

g. Group specific antigen ( gag ) helps in the formation of capsid protein. Polymerase ( pol ) encodes message for the formation of reverse transcriptase. Envelope ( env ) gene is associated with the formation of gp120 and gp41. tax/rex are the regions which encodes the factors involved in transactivation and other regulatory functions.