Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

On the basis of morphologic and immunophenotypic studies, it is generally accepted that the lymphocyte population in thymomas is not neoplastic. We studied 10 thymomas with restriction endonuclease and Southern blot/DNA hybridization methods in an attempt to provide genotypic evidence in support of this hypothesis. The clinical, gross, and microscopic features of each case were reviewed and found to be entirely consistent with the diagnosis of thymoma. In addition to conventional histologic methods, we also studied each tumor by immunohistologic techniques. The lymphocytes generally had an immunotype characteristic of immature cortical thymocytes, and the epithelial cells were uniformly stained by antikeratin antibodies. DNA probes for the T-cell receptor beta-chain gene and immunoglobulin genes (C kappa, C lambda, and JH) were used in the genotypic studies. No gene rearrangements were detected in any of the thymomas. This study provides additional evidence that clonal proliferations of T or B lymphocytes are not present in thymomas; therefore, these cells are almost certainly not neoplastic. The results also provide a basis for the effective use of restriction endonuclease and Southern blot/DNA hybridization analysis in the differential diagnosis of non-Hodgkin's lymphoma and thymoma.
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PMID:Immunoglobulin and T-cell receptor genes in thymomas: genotypic evidence supporting the nonneoplastic nature of the lymphocytic component. 283 Nov 35

We isolated and characterized a type B thymotropic retrovirus (DMBA-LV) which is highly related to mouse mammary tumor virus (MMTV) isolates and which induces T-cell thymomas with a high incidence and a very short latent period. Regions of nonhomology between the DMBA-LV genome and the MMTV genome were identified by heteroduplex mapping and nucleotide sequence studies. In the electron microscope heteroduplex mapping studies the EcoRI-generated 5' and 3' fragments of the DMBA-LV genome were compared with the corresponding fragments of the MMTV (C3H and GR) genome isolated from mammary tumors. The results indicated that DMBA-LV contained a region of nonhomologous nucleotide sequences in the 3' half of the U3 region of the long terminal repeat (LTR). Nucleotide sequence studies confirmed these results and showed that in this region 440 nucleotides of the MMTV (C3H) sequences were deleted and substituted with a segment of 122 nucleotides. This substituted segment in the form of a tandem repeat structure contained nucleotide sequences derived exclusively from sequences which flanked the substitution loop. The distal glucocorticoid regulatory element was unaltered, and two additional copies of the distal glucocorticoid regulatory element-binding site were present in the substituted region. The restriction endonuclease map of the reconstructed molecular clone of DMBA-LV was identical to that corresponding to unintegrated linear DMBA-LV DNA present in DMBA-LV-induced tumor cell lines. Since the nucleotide sequences of the LTRs present in four different DMBA-LV proviral copies isolated from a single thymoma were identical, we concluded that they were derived from the same parental virus and that this type B retrovirus containing an alteration in the U3 region of its LTR could induce thymic lymphomas. Thus, DMBA-LV represents the first example of a productively replicating type B retrovirus that contains an LTR modified in the U3 region and that has target cell and disease specificity for T cells.
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PMID:Alterations in the U3 region of the long terminal repeat of an infectious thymotropic type B retrovirus. 283 15

Envelope gp70s were isolated from the thymotropic recombinant viruses related to Moloney murine leukemia virus (RM-M-MuLVs) which were generated by the inoculation of two strains of ecotropic M-MuLV (strain 1869 and temperature-sensitive mutant-1) into BALB/c or CFW/D mice. Chymotrypsin oligopeptide maps of parental ecotropic MuLV, RM-M-MuLV, and inducible xenotropic MuLV showed each of the above virus types had a distinctly characteristic peptide map. The majority of RM-M-MuLV gp70 molecules examined showed a high degree of peptide homology. Data from restriction endonuclease mapping demonstrated that the newly acquired sequences in each of the RM-M-MuLVs were very related and encompassed both the polymerase and the envelope genes. The source of the sequences acquired by the RM-M-MuLV was from endogenous nonecotropic and nonxenotropic proviruses. This suggested that the family of endogenous proviruses which combined with the parental ecotropic virus was either specifically selected or was much more available than other endogenous proviruses. Although slight variations of envelope-specific sequences and peptides existed among various RM-M-MuLV isolates; within a single thymoma, individual clones of tumor cells yielded RM-M-MuLV gp70s which were identical to each other. These findings are discussed within the context of the leukemogenic potential of RM-MuLVs.
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PMID:Thymotropic envelope gene recombinants of Moloney leukemia virus have highly conserved envelope structures. 299 79

Of 17 Moloney murine leukemia virus (MoMuLV)-induced rat thymomas, 2 contained rearrangements in c-myc. In one of these tumors the observed rearrangement was not due to the insertion of an intact MoMuLV provirus. The rearranged c-myc DNA fragment from this thymoma was cloned and examined by restriction endonuclease mapping, hybridization to MoMuLV proviral DNA probes, and DNA sequence analysis. These analyses revealed that the c-myc rearrangement in this tumor was due to the presence of a partially duplicated MoMuLV long terminal repeat (LTR) 5' to c-myc exon 1. The orientation of this LTR structure was opposite to the transcriptional orientation of c-myc. The sequences at the 3' flanking side of the LTR structure were derived from a cellular DNA region which maps to the same chromosome as c-myc (chromosome 7), although to a site distant from this proto-oncogene. These findings present evidence for a homologous recombination event occurring between sequences of two proviruses integrated on the same chromosome, one of which was inserted near the c-myc proto-oncogene. The recombination product contains three copies of the MoMuLV LTR 72-base-pair direct repeat and is associated with a high level of c-myc expression. The reciprocal product of this recombination was not detected. We propose that recombination between homologous sequences may play a significant role in the generation of chromosomal rearrangements and therefore in tumor induction and progression.
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PMID:Recombination between two integrated proviruses, one of which was inserted near c-myc in a retrovirus-induced rat thymoma: implications for tumor progression. 327 24

Integration and amplification of ecotropic and recombinant proviral sequences in high-molecular-weight cellular DNAs from ecotropic Gross virus-accelerated AKR thymomas were analyzed using an ecotropic-specific probe, p400, and an envelope-specific probe, pAKV-5. New ecotropic proviral sequences were detected at three sites in the DNAs from eight Gross virus-accelerated thymomas following EcoRI restriction endonuclease digestion and at six sites following PvuII restriction endonuclease digestion. The integration of these new ecotropic proviral sequences appeared to be random. Recombinant 3' proviral-cellular DNA junction fragments were detected at 30 sites following digestion with EcoRI. These new recombinant fragments ranged in size from 9.0 to 2.5 kb with 6/8 thymoma DNAs containing a fragment of 2.7 kb. PvuII generated new recombinant 3' proviral-cellular junction fragments that ranged in size from 12.5 to 2.1 kb with 5/8 thymoma DNAs containing a fragment of 2.5 kb. It appears that the leukemia-accelerating ecotropic Gross virus is responsible for the generation of a unique 3' recombinant proviral-cellular junction fragment. This fragment can be detected against a background of randomly integrated ecotropic and recombinant proviruses.
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PMID:Specific integration of recombinant proviral sequences in ecotropic Gross virus-accelerated AKR thymomas. 610 May 72

We have measured the binding of highly radioactive (2'-5')pppA4-5[32P]cytidine 3',5'-diphosphate to human, mouse, and rabbit cell and tissue extracts. A binding activity for this oligonucleotide is present in all extracts examined and high levels of this activity are found in some cells of lymphoid origin. In particular, the mouse thymoma cell line W7 has about 10 times higher binding activity than other cell lines. The oligonucleotide is bound with a single high affinity constant, as shown by Scatchard plot analyses. Cell extracts fractionated by centrifugation on glycerol gradients show a single peak of binding activity, which co-sediments with (2'-5')oligo(A)-dependent endoribonuclease (RNase L). This enzyme apparently binds the oligonucleotide, as shown by experiments with an analog of (2'-5')oligo(A) which competes in the binding and inhibits the RNase L. This endonuclease cannot be directly assayed in unfractionated cell or tissue extracts with high levels of other nuclease activities. The binding assay for the oligonucleotide may provide an estimate of RNase L levels in such cell and tissue extracts.
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PMID:2',5'-Oligo(A)-activated endoribonuclease. Tissue distribution and characterization with a binding assay. 728 31