English: HIV-1 is an enveloped icosahedral retrovirus, belonging to the Lentivirus subgroup of Retroviridae family. Its genome is constituted by two identical copies of non-complementary positive single-stranded RNA, enclosed by a capsid composed of several copies of the viral protein p24. The single-stranded RNA is tightly bound to nucleocapsid proteins and enzymes needed for viral replication and assembly such as reverse transcriptase, proteases, ribonuclease and integrase. A matrix composed of the viral protein p17 surrounds the nucleocapsid and this is, in turn, surrounded by the viral envelope containing the surface glycoproteins gp120 and gp41 as protruding spikes. The HIV replication cycle begins with adsorption of the viral particles to CD4 molecules (a member of the immunoglobulin superfamily) on the surface of susceptible cells. The subsequent interaction with a co-receptor belonging to the family of chemokine receptors (CXCR4 or CCR5) plays a major role in membrane fusion and entry. Shortly after entry, subviral particles are partially uncoated in the cytoplasm and initiate the reverse transcription of viral RNA. The newly produced DNA is then transported into the nucleus and integrated into the host DNA by the virus-encoded integrase. The integrated HIV DNA is called provirus. The provirus may remain inactive for a long time, producing few or no new viral particles. The coordinated interaction of the HIV-encoded Tat protein and cellular transcription factors with the RNA polymerase II transcription apparatus starts the production of viral genomic RNA and messenger RNA, which is then spliced into smaller pieces, exported from the nucleus into the cytoplasm and translated into the proteins. In addition to viral structural proteins and enzymes, the HIV genome encodes the regulatory proteins (Rev and Tat, which is secreted by HIV-infected cells) and several accesory proteins: Vif, Vpu, Vpr, Vpx and Nef, playing an important role in the viral replication, disease pathogenesis and immune evasion. At the end of viral replication cycle, envelope polyproteins are transported to the plasma membrane where viral progeny begins assembly and budding from the infected cells. Then, subsequent proteolysis by viral protease generates mature particles.