Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.30.1 (S1 nuclease)
3,660 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have identified a positive modulator within the c-myc first exon downstream of the gene's transcription initiation sites, P1 and P2. We introduced myc-CAT (chloramphenicol acetyltransferase) hybrid genes into three cell lines (BJAB, COS and HeLa) and measured their expression by either CAT enzymatic activity, S1 nuclease protection or by a nuclear 'run-on' transcription assay. Removal of 46 bp from the 3' end of the first exon results in a decrease of myc-CAT expression and P2 activity. A 438-bp exon 1 segment, lacking the normal myc promoters, efficiently drives the expression of SV40 early promoters. We find that this first exon segment efficiently functions as a positive modulator only in its sense orientation, 3' of a nearby promoter. The positive effects of the myc first exon and the SV40 enhancer are complementary.
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PMID:The first exon of the c-myc proto-oncogene contains a novel positive control element. 303 Jul 32

The c-myc gene is rearranged in a subset of feline T-cell lymphosarcomas. Detailed mapping of c-myc rearrangements showed that some result from feline leukaemia virus (FeLV) proviral integration within or upstream of c-myc, but one case involves a complex 3' alteration and amplification which is apparently not directly virus-induced. S1 nuclease mapping of RNA from normal cells using c-myc probes revealed two presumptive 5' ends, each corresponding to a promoter-like sequence (P1 and P2), and a major 3' discontinuity which mapped to the 3'-most of two possible polyadenylation signals. Analysis of RNA from a series of tumours revealed different modes of c-myc expression. All tumours produced P1 and P2 transcripts with apparently normal structure except for one case where an insertion in intron 1 displaced exon 1 sequences. The abundance ratio of P1/P2 transcripts varied considerably and was high in tumours which carry a rearrangement adjacent to c-myc, but some other T-cell tumours with no apparent myc alteration displayed an equally high ratio. However, a consistent feature was the lack of detectable RNA from normal c-myc alleles in tumours which express a rearranged c-myc allele or a transduced FeLV v-myc gene. We suggest that this may prove to be a useful indicator of the presence of an oncogenically active myc gene, whether this is a rearranged c-myc or transduced v-myc sequence.
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PMID:Altered structure and expression of c-myc in feline T-cell tumours. 303 89

A tumorigenic human hepatoma cell line, Hep G2, has been shown to have high steady-state levels of c-myc transcripts compared to normal human liver. We have now characterized c-myc expression in Hep G2 cells with regard to message stability, gene rearrangements, gene amplification, chromosomal translocations, promoter utilization, and the effects of protein synthesis inhibitors. We have determined that the half-life of the Hep G2 c-myc transcript is approximately 20 min and conclude that the high steady-state level of c-myc mRNA is not the result of a specific stabilization of the c-myc message but probably results from increased c-myc gene transcription. c-myc expression in Hep G2 cells appears to be constitutive, since it remains constant in different cell growth states (log phase versus nondividing cells). The high constitutive expression of the c-myc gene in Hep G2 cells could not be explained by gene amplification, gene rearrangements, or chromosomal translocations. However, based on an S1 nuclease protection assay, the P1/P2 promoter utilization ratio is approximately 1/1 which differs from the 1/5 P1/P2 ratio observed in normal human liver. Treatment with cycloheximide, a protein synthesis inhibitor, does not superinduce Hep G2 c-myc transcription based on transcription "run on" and RNA slot blot analysis. However, cycloheximide treatment does exert a posttranscriptional effect involving the specific stabilization of the c-myc message.
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PMID:Analysis of c-myc expression in a human hepatoma cell line. 303 14

We examined the turnover of c-myc RNA in the human promyelocytic cell line HL-60. In whole-cell RNA from rapidly growing cells we observed two major size classes of c-myc RNA, 2.4 and 2.2 kilobases (kb). When HL-60 cells were treated with actinomycin D for 30 min to inhibit transcription, the 2.4-kb c-myc RNA population was rapidly degraded, while the 2.2-kb c-myc RNA was degraded much more slowly. S1 nuclease transcript mapping and promoter-specific probes were utilized to show that both the stable 2.2-kb and the labile 2.4-kb c-myc RNA populations have 5' ends at the second promoter site (P2) and 3' ends at the second poly(A) addition site. To examine further possible structural differences between these two RNA populations, we fractionated RNA on an oligo(dT)-cellulose column to separate RNAs that contained long poly(A) tails from those which did not. We found that the labile 2.4-kb c-myc RNA population bound to oligo(dT)-cellulose, while the more stable 2.2-kb c-myc RNA population did not. Preliminary estimates of their half-lives (t1/2) showed that the poly(A)+ c-myc RNA had a t1/2 of 12 min, while the c-myc RNA that did not bind to oligo(dT)-cellulose had a t1/2 of greater than 1 h. Several other cell types contain both poly(A)+ and nonpoly(A)+ c-myc RNAs including HeLa cells, normal human bone marrow cells, and normal mouse fetal liver cells. In agreement with the results in HL-60 cell, HeLa cell poly(A)+ c-myc RNA was more labile than c-myc RNA that lacked poly(A). The stable, nonpoly(A)+ c-myc RNA population may be important in the posttranscriptional regulation of c-myc expression.
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PMID:Relatively stable population of c-myc RNA that lacks long poly(A). 303 42

To gain further insight into the mechanism of age-associated loss of T cell proliferative responses to mitogenic lectins, we measured c-myc specific mRNA accumulation in Con A-stimulated cultures of spleen cells from old and young mice using Northern blot and S1 nuclease protection analyses. Aging led to a consistent decline (an average of approximately 60%) in the level of c-myc mRNA in stimulated cells. The time course for c-myc RNA accumulation was similar for old and young mice. Nuclear runoff experiments showed that mitogen stimulation leads to an equivalent increase in transcription of the c-myc gene in T cells from old and young mice. Furthermore, in the presence of 5,6-dichlorobenzimidazole riboside, a selective inhibitor of RNA polymerase II, c-myc mRNA decayed with equal kinetics in cells from mice of different ages. These results show that lymphocytes from aged mice exhibit defects in gene expression very early in the activation process and suggest that these deficits may involve, at least for some genes, alterations in post-transcriptional processing.
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PMID:Defective T lymphocytes in old mice. Diminished production of mature c-myc RNA after mitogen exposure not attributable to alterations in transcription or RNA stability. 328 Jun 82

We have investigated the mechanism of action of IL 1 on T cell activation. For this purpose, we analyzed the content of specific messenger RNA for lymphokines and other genes that are associated with T cell activation in the murine IL 1-dependent T cell lymphoma LBRM33-1A5. Using cloned genes for IL 2, IL 3, TGF-beta, TY5, IL 2 receptor, Ly-1, c-myc, and p53 as probes in the S1 nuclease protection assay, we compared the amount of specific transcripts among total RNA prepared from unstimulated cells, IL 1 alpha or PHA-stimulated cells, and PHA plus IL 1 alpha-stimulated cells. IL 1 alpha augmented the PHA-induced accumulation of IL 2 mRNA with a magnitude comparable to the amount of IL 2 produced, suggesting that IL 1 alpha modulates IL 2 gene expression at the RNA level. Similar results were obtained with IL 3. We also observed that Ly-1 mRNA appears after PHA treatment and its accumulation was augmented by IL 1 alpha addition. On the basis of the effects of IL 1 alpha and/or PHA treatments on gene expression, we classified these genes into four groups. In all cases, IL 1 alpha seemed to affect mRNA levels quantitatively. These observations support previously described characteristics of this cytokine as a co-stimulator of T cell activation.
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PMID:Interleukin 1 modulates messenger RNA levels of lymphokines and of other molecules associated with T cell activation in the T cell lymphoma LBRM33-1A5. 349 73

The chicken c-myc gene, as defined by its homology to the v-myc gene of MC29 virus, is comprised of two exons. Using the techniques of runoff transcription, primer extension, and S1 nuclease protection, we demonstrate that there is a third c-myc exon of approximately equal to 345 base pairs (bp) located 0.7 kbp upstream of the 5' end of the v-myc homology. This first exon is transcribed and present in myc mRNA in normal chicken cells. We also examined RNA from five cell lines derived from avian leukosis virus-induced bursal lymphomas. In all these lines, the level of transcription of the 2.2- to 2.5-kbp myc mRNA is increased 30- to 60-fold over normal cells. The myc mRNA in four of these lines also contains increased levels of the first noncoding exon, and evidence is presented that the long terminal repeat (LTR) in the vicinity of c-myc is functioning as an enhancer of c-myc transcription rather than as a promoter in several of these cell lines. In two cell lines in which the viral LTR has integrated between the first and second exons in the proper orientation for downstream promotion of myc, the LTR does not exhibit promoter function. The pattern of c-myc transcription observed by others in a vast majority of avian leukosis virus-induced neoplasms is not observed in any of the five cell lines examined.
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PMID:Transcription of three c-myc exons is enhanced in chicken bursal lymphoma cell lines. 385 49

HL-60 cells have an elevated level of cellular myc RNA due to an amplified c-myc gene. Subsequent to chemically induced differentiation of HL-60 cells, both cellular myc RNA levels (Grosso, L. E., and Pitot, H. C., Biochem. Biophys. Res. Commun., 119: 473, 1984) and myc-specific transcription decrease (Grosso, L. E., and Pitot, H. C., Cancer Res., 45: 847-850, 1985). We have compared the primary DNA structure, DNA methylation, and S1 nuclease sensitivity of the myc protooncogene in HL-60 cells before and after chemically induced differentiation. We find no change in the structure or methylation of the c-myc gene. The protooncogene is hypomethylated at CCGG sequences in the 5' region but is extensively methylated at sites detected by sequences homologous to the 3' exon or 3' flanking sequences. Four S1 nuclease-sensitive sites are detected prior to differentiation. After the induction of either myeloid or monocytic differentiation, three of the S1 nuclease-sensitive sites are present. The presence of the fourth S1 nuclease-sensitive site correlates with the transcriptional activity of this gene.
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PMID:Chromatin structure of the c-myc gene in HL-60 cells during alterations of transcriptional activity. 386 Dec 42

In many mouse plasmacytomas, the active c-myc gene has been truncated by chromosome translocation with the resultant severance of the protein-coding sequence from the normal promoter. Transcripts of such truncated c-myc genes were analyzed by Northern blotting, nuclease S1 mapping, primer extension assays and cDNA cloning. We conclude that transcription originates from multiple initiation sites on both c-myc coding and non-coding strands with the two-sets of transcripts derived from adjacent but essentially non-overlapping regions located greater than 1 kb from the translocation junction. In X63Ag8, where c-myc is translocated to the immunoglobulin C gamma 2b gene, the c-myc non-coding strand transcripts include the translocation junction and then splice directly into the gamma 2b CH1 exon. We propose that chromosome translocation activates a cryptic promoter in the first intron and that the heterogeneously initiated, bipolar transcription reflects the absence of a suitably placed TATA box element.
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PMID:Chromosome translocation activates heterogeneously initiated, bipolar transcription of a mouse c-myc gene. 392 91

We have investigated whether the translocated and the untranslocated human c-myc oncogenes of Burkitt lymphoma cells are equally or differentially expressed in host mouse B cells. The human c-myc mRNA levels in somatic cell hybrids between mouse plasmacytoma cells and Burkitt lymphoma cells with either the t(8;14) or the t(2;8) chromosome translocation were determined by using the nuclease S1 protection procedure. Although both the human parental lines and the hybrid cells carrying the translocated c-muc oncogene expressed high levels of human specific c-myc transcripts, the hybrid cells carrying the untranslocated c-myc gene on normal chromosome 8 did not contain human specific c-myc mRNA. These results suggest that the translocated human c-myc oncogene has escaped the normal transcriptional control to which the untranslocated c-myc gene remains subjected. This interpretation is also supported by the finding that the expression of the c-myc genes of lymphoblastoid cells and of HL-60 promyelocytic leukemia cells are repressed when they are transferred into a mouse plasmacytoma background. The ability of the translocated c-myc oncogene to escape the normal transcriptional control occurring in B cells may be important for the expression of B cell neoplasia in mouse and man. We have also transferred the Burkitt 14q+ chromosome carrying a translocated c-myc oncogene into mouse LM-TK- fibroblasts and studied the levels of human c-myc transcripts in the hybrids. Because the levels of human c-myc transcripts in the fibroblast hybrids are dramatically decreased in comparison to the plasmacytoma hybrids, we conclude that the levels of transcripts of the translocated c-myc oncogene depend on the differentiated state of the cells harboring the translocated chromosome.
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PMID:Differential expression of the normal and of the translocated human c-myc oncogenes in B cells. 630 54


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