HTLV-III gag protein is processed in yeast cells by the virus pol-protease

The gag-pol gene of HTLV-III (human T-lymphotropic virus), the virus linked to AIDS (acquired immune deficiency syndrome), was expressed in yeast, and processing of the gag precursor into proteins of the same size as those in the virion was observed. Processing of the gag gene in yeast cells mimics the process that naturally occurs in mammalian cells during maturation of virions. Therefore it was possible to perform mutational analysis of the virus genome to localize the gene that codes for the protease function to the amino terminal coding region of the pol gene. Since this region overlaps the gag gene, it is likely that ribosomal frameshifting occurs from gag to pol. Antibodies in all of the AIDS patients' sera tested recognized the yeast synthesized gag proteins, although the sera showed differences in relative reactivity to the individual gag proteins and the precursor. This yeast system should be valuable not only for production of viral proteins for diagnostic or vaccine purposes but also for analysis of the genetics and biochemistry of viral gene functions--parameters that are difficult to study otherwise with this virus.     

A synthetic HIV-1 protease inhibitor with antiviral activity arrests HIV-like particle maturation

A synthetic peptidemimetic substrate of the human immunodeficiency virus 1 (HIV-1) protease with a nonhydrolyzable pseudodipeptidyl insert at the protease cleavage site was prepared. The peptide U-81749 inhibited recombinant HIV-1 protease in vitro (inhibition constant Ki of 70 nanomolar) and HIV-1 replication in human peripheral blood lymphocytes (inhibitory concentration IC50 of 0.1 to 1 micromolar). Moreover, 10 micromolar concentrations of U-81749 significantly inhibited proteolysis of the HIV-1 gag polyprotein (p55) to the mature viral structural proteins p24 and p17 in cells infected with a recombinant vaccinia virus expressing the HIV-1 gag-pol genes. The HIV-1 like particles released from inhibitor-treated cells contained almost exclusively p55 and other gag precursors, but not p24. Incubation of HIV-like particles recovered from drug-treated cultures in drug-free medium indicated that inhibition of p55 proteolysis was at least partially reversible, suggesting that U-81749 was present within the particles.     

Expression in Escherichia coli of open reading frame gene segments of HTLV-III

Human T-cell lymphotropic virus type III (HTLV-III), the causative agent of the acquired immune deficiency syndrome (AIDS), was recently isolated and its genomic structure analyzed by DNA cloning methods. In the studies reported here a combined cloning and expression system was used to identify HTLV-III encoded peptides that react immunologically with antibodies in sera from AIDS patients. Cloned HTLV-III DNA was sheared into approximately 500-base-pair fragments and inserted into an "open reading frame" expression vector, pMR100. The inserted DNA was expressed in Escherichia coli transformants as a polypeptide fused to the lambda CI protein at its amino terminus and to beta-galactosidase at its carboxyl terminus. Sera from AIDS patients containing antibodies to HTLV-III were then used to screen for immunoreactive fusion proteins. Twenty clones, each specifying a fusion protein strongly reactive with AIDS serum, were identified. DNA sequence analysis indicated that the HTLV-III fragments were derived from the open reading frame DNA segments corresponding to the gag and pol gene coding regions and also the large open reading frame region (env-lor) located near the 3' end of the viral genome.     

Isolation and characterization of a novel protein (X-ORF product) from SIV and HIV-2

A protein designated p14 was purified from a simian immunodeficiency virus (SIVMne) and was shown by amino acid sequence analysis to be nearly identical to the predicted translational product of a unique open reading frame (X-ORF) in the nucleotide sequences of SIVmac and human immunodeficiency virus type 2 (HIV-2). Thus the X-ORF is proven to be a new retroviral gene. The p14 is present in SIVMne in molar amounts equivalent to those of the gag proteins. This is the first example of a retrovirus that contains a substantial quantity of a viral protein that is not a product of the gag, pro, pol, or env genes. SIV p14 and its homolog in HIV-2 may function as nucleic acid binding proteins since purified p14 binds to single-stranded nucleic acids in vitro. Antisera to the purified protein detected p14 in SIVMne, SIVmac, and a homologous protein (16 kilodaltons) in HIV-2 but did not react with HIV-1. Diagnostic procedures based on this novel protein will distinguish between HIV-1 and HIV-2.     

HTLV x-gene product: requirement for the env methionine initiation codon

The human T-cell leukemia viruses (HTLV) are replication-competent retroviruses whose genomes contain gag, pol, and env genes as well as a fourth gene, termed x, which is believed to be the transforming gene of HTLV. The product of the x gene is now shown to be encoded by a 2.1-kilobase messenger RNA derived by splicing of at least two introns. By means of S1 nuclease mapping of this RNA and nucleic acid sequence analysis of a complementary DNA clone, the complete primary structure of the x-gene product has been determined. It is encoded by sequences containing the env initiation codon and one nucleotide of the next codon spliced to the major open reading frame of the HTLV-I and HTLV-II x gene.     

RNA required for import of precursor proteins into mitochondria

A cytoplasmic RNA moiety is necessary for posttranslational uptake of nuclear-encoded mammalian proteins destined for the mitochondrial matrix. Post-translational addition of ribonuclease to a reticulocyte lysate-programmed cell-free translation mixture inhibited subsequent import of six different mitochondrial matrix enzyme precursors into rat liver mitochondria. The required RNA is highly protected, as indicated by the high concentrations of ribonuclease necessary to produce this inhibition. The dependence of the inhibitory effect on temperature, duration of exposure to ribonuclease, and availability of divalent cations is characteristic of the nuclease susceptibility of ribonucleoproteins. The ribonuclease-sensitive component was found in a 400-kilodalton fraction which contains the mitochondrial protein precursors.     

A continuous cell-free translation system capable of producing polypeptides in high yield

A cell-free translation system has been constructed that uses a continuous flow of the feeding buffer [including amino acids, adenosine triphosphate (ATP), and guanosine triphosphate (GTP)] through the reaction mixture and a continuous removal of a polypeptide product. Both prokaryotic (Escherichia coli) and eukaryotic (wheat embryos, Triticum sp.) versions of the system have been tested. In both cases the system has proven active for long times, synthesizing polypeptides at a high constant rate for tens of hours. With the use of MS2 phage RNA or brome mosaic virus RNA 4 as templates, 100 copies of viral coat proteins per RNA were synthesized for 20 hours in the prokaryotic or eukaryotic system, respectively. With synthetic calcitonin messenger RNA, 150 to 300 copies of calcitonin polypeptide were produced per messenger RNA in both types of continuous translation systems for 40 hours.     

Template activity of RNA from antibody-producing tissues

An RNA fraction, which represents a small percentage of cellular RNA and which has the characteristics of nuclear messenger RNA, has been isolated from the spleen and lymph nodes of immunized rats by successive phenol extractions of these tissues at increasing temperatures. This fraction increased the amount of protein synthesized in a cell-free extract of Escherichia coli as much as 35 times and directed the synthesis of proteins different from those of E. coli.     

Replicative and cytopathic potential of HTLV-III/LAV with sor gene deletions

The genome of the human T-lymphotropic virus type III (HTLV-III/LAV) has the potential to encode at least three polypeptides in addition to those encoded by the gag, pol, and env genes. In this study, the product of the sor (short open reading frame) region, which overlaps the 3' end of the pol gene, was found to be a protein with a molecular weight of 23,000. An assay was developed for testing the ability of cloned HTLV-III proviruses to produce viruses cytopathic for T4+ lymphocytes. In the cell line used, C8166, neither the HTLV-III sor gene product nor the complete 3'-orf gene product were necessary for the replication or cytopathic effects of the HTLV-III.     

Antibodies to human c-myc oncogene product: evidence of an evolutionarily conserved protein induced during cell proliferation

Antisera to a synthetic c-myc peptide and to c-myc antigens synthesized from various portions of the human gene expressed in Escherichia coli were used in order to characterize the protein product of the human c-myc oncogene. Although the deduced molecular weight of the human c-myc protein is 49,000, these antisera precipitate a protein from human cells that migrates in sodium dodecyl sulfate-polyacrylamide gel as if its molecular weight were 65,000. In addition, the mouse c-myc protein, whether synthesized in cells or in a cell-free system directed by pure, synthetic messenger RNA, has analogous properties and is immunoprecipitated by the antiserum to the human c-myc protein. Similar proteins are immunoprecipitated from monkey, rat, hamster, and frog cells, suggesting evolutionary conservation of antigenic structure of the c-myc protein among vertebrates. In addition, and in a manner consistent with the behavior of its messenger RNA, the immunoprecipitable c-myc protein is sharply induced by the action of mitogens on resting human T cells.     

Unexpectedly high levels of HIV-1 RNA and protein synthesis in a cytocidal infection

The expression of a laboratory strain of HIV-1 (HTLV-IIIB) has been studied in mitogen-stimulated peripheral blood lymphocytes (PBLs) and in two lymphoid cell lines (CEM cells and C8166 cells). HIV-expressing cells contained from 300,000 to 2,500,000 copies of viral RNA per cell. Near-synchronous expression of an active infection could be achieved in C8166 cells. In these cells, the high copy numbers of viral RNA used as much as 40% of total protein synthesis for the production of viral gag protein, with high levels of viral RNA and protein synthesis preceding cell death by 2 to 4 days.     

Cell-free protein synthesis: effects of age and state of ribosomal aggregation

In cell-free extracts derived from Streptococcus faecalis, protein synthesis directed by endogenous messenger RNA increases as the culture ages. The increased activity is accompanied by an increase in the percentage of membranebound ribosomes and by a decrease in ribosomal monomers and subunits. These changes progress against a background of structural and compositional modifications in the membrane. Membrane modifications possibly related to endogenously directed protein synthesis in cell-free extracts include: (i) decreased specific activity of a membrane-associated polynucleotide phosphorylase capable of polysome degradation, and (ii) increased concentrations of certain phospholipids.     

Nucleotide sequence of SRV-1, a type D simian acquired immune deficiency syndrome retrovirus

Simian acquired immune deficiency syndrome (SAIDS) in the macaque genus of monkeys at the California Primate Research Center is apparently caused by infection by a type D retrovirus. The complete nucleotide sequence (8173 base pairs) of a molecular clone of the prototype SAIDS virus isolate, SRV-1, reveals a typical retrovirus structure with long terminal repeats (346 base pairs) and open reading frames for the gag (663 codons), pol (867 codons), and env (605 codons) genes. SRV-1 also has a separate open reading frame of 314 codons between the gag and pol genes that defines the viral protease gene (prt) and a short open reading frame of unknown significance downstream from the env gene. The SRV-1 protease region shows a high degree of homology to its counterpart in the hamster intracisternal A-type particle genome; both these protease genes are about twice as long as the analogous region of other retroviruses. SRV-1 has no notable similarity in either genetic organization or sequence to the human AIDS retroviruses.     

Detergent-solubilized RNA polymerase from cells infected with foot-and-mouth disease virus

The foot-and-mouth disease virus RNA polymerase complex was dissociated from cellular membranes with deoxycholate in the presence of dextran sulfate. The soluble polymerase complex was active in the cell-free synthesis of virus-specific RNA; solubilization of the complex permitted direct analysis of the cell-free reaction mixtures without recourse to RNA extraction. A major RNA-containing component found early during cell-free incubation ranged from approximately 140 to 300S. The final major products of the cell-free system were 37S virus RNA, 20S ribonuclease-resistant RNA, and a 50S component containing RNA.