Showing papers by "David Baltimore published in 1978"

Identification of an Abelson murine leukemia virus-encoded protein present in transformed fibroblast and lymphoid cells

Abstract: Extracts from lymphoid and fibroblast cell lines transformed by Abelson murine leukemia virus (A-MuLV) contain a protein of molecular weight 120,000 (P120). Immunoprecipitation with specific sera shows that P120 contains regions homologous to the 5'-terminal segment of the MULV gag gene complex--p15, p12, and at least part of p30--but lacks detectable determinants of p10, reverse transcriptase, and the envelope glycoprotein. P120 is phosphorylated and has an intracellular half-life of 3--6 hr. In vitro translation of virion RNA from A-MuLV, with Moloney MuLV as helper, yields a product of molecular weight 120,000 with serological reactivity similar to that of the cellular P120. Translation of the RNA from the helper gave no P120. P120 is expressed in all lymphoid and fibroblastic cell lines we have tested that were transformed by A-MuLV but is not detectable in a lymphoid line in which the A-MuLV genome was established by infection but was not responsible for the transformation. Expression of P120 is selectively retained in clones of A-MuLV-transformed lymphocytes that convert to a nonproducer state after loss of expression of helper MuLV intracellular precursors. These results suggest that the P120 product of the A-MuLV genome may be responsible for maintenance of the transformed phenotype of lymphoid and fibroblast cells transformed by the virus.

Terminal Transferase as a Predictor of Initial Responsiveness to Vincristine and Prednisone in Blastic Chronic Myelogenous Leukemia

Abstract: We undertook a prospective trial to evaluate terminal deoxynucleotidyl transferase activity as a predictor of responsiveness to vincristine and prednisone in 22 Philadelphia-Chromosome-Positive patients with blastic chronic myelogenous leukemia. Thirteen patients were transferase positive, and nine negative. None of the nine negative patients responded, whereas eight of the 13 positive (P = 0.004) responded with complete clearing of peripheral blood blast cells and a return of normal marrow cellularity with less than 5 per cent blast cells. Among transferase-positive patients under 50 years of age the response rate was 78 per cent. Blast-cell morphology (i.e., lymphoblastic versus myeloblastic) had no significant correlation with either responsiveness or terminal transferase activity. The results of this study suggest that responsiveness to vincristine and prednisone in blastic chronic myelogenous leukemia is confined to patients whose leukemic cells are transferase positive. (N Engl J Med 298:81...

Relationship of retrovirus polyprotein cleavages to virion maturation studied with temperature-sensitive murine leukemia virus mutants.

Abstract: Murine leukemia virus mutants ts3 (Moloney) and ts24 (Rauscher) both formed late-budding structures on the cell membrane at restrictive temperature. They both accumulated core polyproteins Pr65gag and Pr180gag-pol in cell membranes, but the envelope precursor was rapidly turned over. After shift to permissive temperature in the presence of cycloheximide, the accumulated precursors were sequentially cleaved via discrete intermediates both during the final stages of the budding process and in newly released virions to yield the finished virion core proteins and reverse transcriptase. The precursor form of reverse transcriptase was not enzymatically active and became activated partially or entirely inside released virions.

Inhibition of translation by poliovirus: inactivation of a specific initiation factor.

Abstract: Translation of vesicular stomatitis virus (VSV) mRNA, like host mRNA translation, is inhibited in cells infected with poliovirus To study the mechanism of poliovirus-induced inhibition of protein synthesis, we prepared extracts from poliovirus-infected and uninfected HeLa cells Poliovirus mRNA was translated in lysates from both infected and uninfected cells, while VSV mRNA was translated only in the lysate from uninfected cells Addition of purified translation initiation factors to the extract from infected cells showed that one factor, eIF-4B, could restore VSV mRNA translation in the infected lysate, but did not increase poliovirus mRNA translation Further experiments involving translation of VSV mRNA in mixed extracts from poliovirus-infected and uninfected cells showed (i) that there was not an excess of an inhibitor of VSV mRNA translation in the infected lysate, but (ii) that an acitivity that caused a slow inactivation of eIF-4B was present in the infected lysate Inactivation of eIF-4B appears to be the mechanism by which poliovirus infection causes a selective inhibition of translation

Identification of a protein linked to nascent poliovirus RNA and to the polyuridylic acid of negative-strand RNA.

Abstract: A protein similar to that previously demonstrated on poliovirus RNA and replicative intermediate RNA (VPg) was found on all sizes of nascent viral RNA molecules and on the polyuridylic acid isolated from negative-strand RNA. ^(32)P-labeled nascent chains were released from their template RNA and fractionated by exclusion chromatography on agarose. Fingerprint analysis using two-dimensional polyacrylamide gels of RNase T1 oligonucleotides derived from nascent chains of different lengths showed that a size fractionation of nascent chains was achieved. VPg was recovered from nascent chains varying in length from 7,500 nucleotides (full-sized RNA) to about 500 nucleotides. No other type of 5' terminus could be demonstrated on nascent RNA, and the yield of VPg was consistent with one molecule of the protein on each nascent chain. These results are consistent with the concept that the protein is added to the 5' end of the growing RNA chains at a very early stage, possibly as a primer of RNA synthesis. Analysis of the polyuridylic acid tract isolated from the replicative intermediate and double-stranded RNAs indicated that a protein of the same size as that found on the nascent chains and virion RNA is also linked to the negative-strand RNAs. It is likely that a similar mechanism is responsible for initiation of synthesis of both plus- and minus-strand RNAs.

The effect of helper virus on Abelson virus-induced transformation of lymphoid cells.

Abstract: Abelson murine leukemia virus (A-MuLV)-transformed fibroblast nonproducer cells were used to prepare A-MuLV stocks containing a number of different helper viruses. The oncogenicity of the A-MuLV stocks was tested by animal inoculation and their ability to transform normal mouse bone marrow cells was measured in vitro. All of the A-MuLV stocks transformed fibroblast cells efficiently. However, only A-MuLV stocks prepared with helper viruses that are highly oncogenic were efficient in vivo and in vitro in hematopoietic cell transformation. In addition, inefficient helpers did not establish a stable infection in lymphoid nonproducer cells. Thus, helper virus has a more central role in lymphoid cell transformation than in fibroblast cell transformation.

Assignment of the receptor for ecotropic murine leukemia virus to mouse chromosome 5

Abstract: The gene for the receptor for ecotropic murine leukemia virus (Rev) has been assigned to mouse chromosome 5. This determination was made possible by an analysis of somatic cell hybrids between mouse and Chinese hamster cells. The parents of these hybrids were A/HeJ or Mus poschiavinus peritoneal exudate cells or BALB/c primary embryo fibroblasts and E36, a Chinese hamster lung fibroblast deficient in hypoxanthine guanine phosphoribosyltransferase. Segregation of mouse chromosomes in these hybrids was analyzed by chromosome banding and isozyme expression. Cells were tested for their ability to absorb and replicate vesicular stomatitis virus (murine leukemia virus [MuLV]) pseudotype particles and ecotropic MuLV as measured by the XC test. The presence of chromosome 5 was essential for receptor expression as determined by three statistical procedures. Segregation of the receptor for ecotropic murine leukemia virus was also followed in two series of subclones. In both, receptor expression was syntenic with phosphoglucomutase-1, an isozyme which has been mapped to mouse chromosome 5.

Vesicular stomatitis virus glycoprotein is necessary for H-2-restricted lysis of infected cells by cytotoxic T lymphocytes.

Abstract: Vesicular stomatitis virus (VSV) elicited cytotoxic thymus-derived lymphocytes (CTLs) in mice of the BALB/c and three congenic strains (BALB.b, BALB.k, BALB.HTG). CTL lysis of VSV-infected fibroblasts from the four strains was restricted by the target cells' major histocompatibility complex (H-2). Target cells were also infected with two temperature-sensitive mutants of VSV, tsM and tsG in which, respectively, the viral matrix protein and glycoprotein are not expressed at 39 degrees (restrictive temperature) on the infected cell's surface membrane. At the restrictive temperature, cells infected with wild-type VSV or tsM were lysed by CTLs, but cells infected with tsG were not. The requirement for the glycoprotein on the target cell was also evident from the ability of antisera to the glycoprotein to block completely CTL lysis of VSV-infected cells.

Leukemogenicity of Clonal Isolates of Murine Leukemia Viruses

Abstract: The leukemogenicity of three types of cloned, in vitro grown murine retroviruses was studied. Two Moloney virus clones caused leukemia, as did five clones of the B-tropic endogenous virus of BALB/c mice. Neither of two clones of N-tropic BALB/c virus caused leukemia in Fv-1n/n mice, and the viruses were not recoverable from the animals. The ability to induce leukemia therefore appeared to reside in the genome of at least certain nondefective murine retroviruses.

Retroviruses and Cancer

Abstract: All RNA viruses that cause cancer under natural conditions fall into the “retro” category, meaning that the first step in their replication is the “reverse transcription” of RNA into DNA. This peculiarity of their biologic behavior has helped explain other intriguing features of these viruses and opened new directions for future research into the role of viruses in altering the infected cell's genetic material and in oncogenesis.