title: Properties of intracytoplasmic A particles isolated from oncornavirus-producing human cells.
abstract: A particles with the diameter of 70 to 80 nm were isolated from the cytoplasm of HEp-2, HeLa, and AO cells producing oncornavirus of Mason-Pfizer-like type. Most of the A particles banded at 1.23 to 1.24 g/ml, whereas 3 to 10% banded at 1.29 g/ml in equilibrium sucrose gradients. They banded at 1.30 g/ml in CsCl gradients suggesting that they contained 8% RNA. Individual A particles sedimented at 200 to 250S in velocity sucrose gradients, but their significant part was found aggregated and sedimented at more than 300S. They were resistant to RNase digestion. A particles possessed polymerase activity which was preferentially activated by Mn(2+) rather than by Mg(2+), the RNA template being 60S RNA. Cross-hybridization with two DNA products and immunoassay showed that A particles and Mason-Pfizer-like oncornavirus produced by the same cells contained neither homological RNA sequences nor common antigens, suggesting that A particles are not intracellular precursors of Mason-Pfizer-like oncornavirus but represent an independent oncornavirus. Hybridization of A particle RNA with excess of cellular DNA revealed about 20 proviral copies per HEp-2 cell genome and no proviral copies in human embryo and placenta cell genomes.
mesh_terms: D000956:Antigens, Viral / Q000032:analysis; D002294:Carcinoma, Squamous Cell; D002458:Cell Fractionation; D002460:Cell Line; D002478:Cells, Cultured / Q000382:microbiology*; D002499:Centrifugation, Density Gradient; D003593:Cytoplasm / Q000382:microbiology*; D004279:DNA, Viral / Q000096:biosynthesis; D006367:HeLa Cells; D006801:Humans; D005779:Immunodiffusion; D007181:Inclusion Bodies, Viral; D007822:Laryngeal Neoplasms; D008168:Lung / Q000196:embryology; D008854:Microscopy, Electron; D009693:Nucleic Acid Hybridization; D009858:Oncogenic Viruses / Q000201:enzymology / Q000276:immunology / Q000302:isolation & purification; D010761:Phosphorus Radioisotopes; D012367:RNA, Viral; D012194:RNA-Directed DNA Polymerase / Q000378:metabolism; D013698:Templates, Genetic; D014316:Tritium; D014529:Uridine
chemical_list: D000956:Antigens, Viral; D004279:DNA, Viral; D010761:Phosphorus Radioisotopes; D012367:RNA, Viral; D014316:Tritium; D012194:RNA-Directed DNA Polymerase; D014529:Uridine