HIV Replication Cycle

Steps in the HIV Replication Cycle

1. Fusion of the HIV cell to the host cell surface.
2. HIV RNA, reverse transcriptase, integrase, and other viral proteins enter the host cell.
3. Viral DNA is formed by reverse transcription.
4. Viral DNA is transported across the nucleus and integrates into the host DNA.
5. New viral RNA is used as genomic RNA and to make viral proteins.
6. New viral RNA and proteins move to cell surface and a new, immature, HIV virus forms.
7. The virus matures by protease releasing individual HIV proteins.

Credit: NIAID

HIV Replication Cycle Glossary

CD4 – a large glycoprotein that is found on the surface of helper T cells, regulatory T cells, monocytes, and dendritic cells. Its natural function is as a co–receptor that assists the T cell receptor (TCR) to activate its T cell following an interaction with an antigen presenting cell. CD4 is a primary receptor used by HIV–1 to gain entry into host T cells.

Co–receptor (CCR5 or CXCR4) – protein molecules on the surface of lymphocytes or monocytes that bind to the gp120 protein of HIV and facilitate, usually with CD4, entry of viral nucleic acid and proteins into the cell.

DNA (deoxyribonucleic acid) – is a nucleic acid that contains the molecular basis of heredity for all known living organisms and some viruses and is found in the nuclei and mitochondria of eukaryotes. Chemically DNA consists of two polymer strands of units called nucleotides made up of one of four possible bases plus sugar and phosphate groups. The polymers are joined at the bases by hydrogen bonds to form a double helix structure.

Fusion of virus and cell membranes – a merging of cell and virus membranes that permits HIV proteins and nucleic acids to enter the host cell.

Genomic RNA – the nucleic acid that contains all of the hereditary information of a virus, and is found in a mature virion.

gp120 – an HIV glycoprotein having a molecular weight of 120 that protrudes from the outer surface of the virion. This glycoprotein binds to a CD4 receptor on a T cell to facilitate entry of viral nucleic acid and proteins into the cell.

HIV (human immunodeficiency virus) – is a lentivirus and a member of the retrovirus family. HIV infects and destroys helper T cells of the immune system causing a marked reduction in their numbers. Loss of CD4 cells leads to generalized failure of the immune system and susceptibility to life threatening opportunistic infections.

Integrase – An enzyme found in retroviruses including HIV that permits the viral DNA to be integrated into the DNA of the infected cell.

Preintegration complex (PIC) – It is composed of viral RNA and proteins (nucleocapsid, p6, Vpr, integrase, and matrix) as well as some host proteins. It functions to reverse transcribe genomic RNA into double stranded DNA prior to integration into the host genomic DNA.

Protease – an enzyme that hydrolyzes or cuts proteins and is important in the final steps of HIV maturation.

Nucleus – a membrane enclosed cellular organelle of eukaryotes that functions to contain the genomic DNA and to regulate gene expression.

Reverse transcriptase – an enzyme found in HIV that creates double stranded DNA using viral RNA as a template and host tRNA as primers.

RNA (ribonucleic acid) – a nucleic acid that differs from DNA in that it contains ribose and uracil as structural components.

RNA virus – a virus that uses RNA as its genetic material and belongs to either Group III, IV, or V of the Baltimore Classification System of Viruses. HIV belongs to Group III, double stranded RNA viruses.

Virion – a single and complete extracellular infective form of a virus that consists of an RNA or DNA core with a protein coat or "envelope".