title: The HIV 'A' (sor) gene product is essential for virus infectivity.
abstract: The genome of the human immunodeficiency virus (HIV) contains several open reading frames (ORFs) not present in other viruses. The 'A' gene, also known as Q2 P'3, ORF-1(4) or sor5, partially overlaps the pol gene; its protein product has a relative molecular mass of 23,000 (Mr 23K) and is present in productively infected cells. The function of this protein is unclear; mutant viruses deleted in 'A' replicate in and kill CD4+ lymphocyte lines, but the high degree of conservation of the deduced amino-acid sequence in nine different HIV isolates (80%) and the presence of analogous genes in HIV-2 and other lentiviruses suggest that the gene function is an important one. Here we describe a mutant virus deficient in the 'A' gene which produces virion particles normally; however, the particles are approximately 1,000 times less infective than wild type. Transcomplementation experiments partially restore infectivity. The mutant virus spreads efficiently when virus-producing cells are co-cultivated with CD4+ lymphocytes, however, indicating that HIV can spread from cell to cell in a mechanism that does not require the 'A' gene product and probably does not require the production of infective virus particles.
mesh_terms: D000595:Amino Acid Sequence; D002450:Cell Communication; D002872:Chromosome Deletion; D003001:Cloning, Molecular; D003110:Colonic Neoplasms / Q000235:genetics; D005816:Genetic Complementation Test; D006678:HIV / Q000235:genetics*; D006801:Humans; D009154:Mutation; D010641:Phenotype; D012194:RNA-Directed DNA Polymerase / Q000378:metabolism; D011995:Recombination, Genetic; D014162:Transfection; D014771:Virion / Q000032:analysis
chemical_list: D012194:RNA-Directed DNA Polymerase