476
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Laub O, Rall L, Bell GI, Rutter WJ. Expression of the human insulin gene in an alternate mammalian cell and in cell extracts. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32369-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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477
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Naylor SL, Sakaguchi AY, Shen LP, Bell GI, Rutter WJ, Shows TB. Polymorphic human somatostatin gene is located on chromosome 3. Proc Natl Acad Sci U S A 1983; 80:2686-9. [PMID: 6133281 PMCID: PMC393892 DOI: 10.1073/pnas.80.9.2686] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Somatostatin is a 14-amino-acid neuropeptide and hormone that inhibits the secretion of several peptide hormones. The human gene for somatostatin SST has been cloned, and the sequence has been determined. This clone was used as a probe in chromosome mapping studies to detect the human somatostatin sequence in human-rodent hybrids. Southern blot analysis of 41 hybrids, including some containing translocations of human chromosomes, placed SST in the q21 leads to qter region of chromosome 3. Human DNAs from unrelated individuals were screened for restriction fragment polymorphisms detectable by the somatostatin gene probe. Two polymorphisms were found: (i) an EcoRI variant located at the 3' end of the gene, found in Caucasian, U.S. Black, and Asian populations with a frequency of approximately 0.10 and (ii) a BamHI variant in the intron, which occurs in Caucasians at a frequency of 0.13.
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478
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Bell GI, Santerre RF, Mullenbach GT. Hamster preproglucagon contains the sequence of glucagon and two related peptides. Nature 1983; 302:716-8. [PMID: 6835407 DOI: 10.1038/302716a0] [Citation(s) in RCA: 420] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Glucagon is a 29-amino acid polypeptide hormone synthesized by the A cells of the endocrine pancreas. Its primary site of action is the liver where it stimulates glycogenolysis, gluconeogenesis and ketogenesis. In mammals, biosynthetic studies have shown that glucagon is derived from a precursor of molecular weight (Mr) approximately 18,000 which is five to six times larger than glucagon. Glucagon-containing polypeptides and immunoreactants of various sizes have also been described from stomach, intestine, brain and salivary gland. Here, we have determined the structure of hamster pancreatic preproglucagon from the sequence of its cDNA. This 180-amino acid precursor contains the sequence of glucagon and two glucagon-like polypeptides arranged in tandem. The precursor also contains the sequences of several non-pancreatic glucagon-containing polypeptides which suggests that, in mammals, both pancreatic and non-pancreatic glucagon and glucagon-containing polypeptides may be derived from a common precursor by tissue-specific processing. We have tentatively identified each of the glucagon-like immunoreactants which have been described with respect to the sequence of proglucagon and have proposed a scheme for the processing of pancreatic proglucagon.
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479
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Scott J, Selby M, Urdea M, Quiroga M, Bell GI, Rutter WJ. Isolation and nucleotide sequence of a cDNA encoding the precursor of mouse nerve growth factor. Nature 1983; 302:538-40. [PMID: 6336309 DOI: 10.1038/302538a0] [Citation(s) in RCA: 391] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Nerve growth factor (NGF) is a polypeptide that enhances survival, nerve fibre outgrowth and neurotransmitter biosynthesis in sympathetic and sensory neurones. Administration of antibodies against NGF to developing animals leads to atrophy of the sympathetic system. NGF is not normally detectable in innervated tissues but ablation of the innervating neurones leads to the production of measurable NGF in the target tissue. After transplantation of the denervated tissue, reinnervation occurs, then NGF decreases to undetectable levels. Thus NGF seems to act as a neurotrophic messenger and its level is regulated by innervating neurones. Because of the minute levels present it is very difficult to study NGF biosynthesis in innervated tissue. However, NGF can be isolated from male mouse submaxillary glands, where it exists in inexplicably high levels. Its amino acid sequence has been determined, and the synthesis of NGF and its larger precursors has been demonstrated in cultured submaxillary glands. We report here the nucleotide sequence of a submaxillary cDNA encoding the mouse NGF precursor (preproNGF). In contrast to previous suppositions the NGF moiety is situated near the carboxyterminus of the polyprotein precursor. It is flanked at the amino-terminus by 187 amino acids which may be cleaved at dibasic residues to generate three peptides; there are only two additional amino acids at the carboxy-terminus.
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480
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Perelson AS, Bell GI. Delivery of lethal hits by cytotoxic T lymphocytes in multicellular conjugates occurs sequentially but at random times. THE JOURNAL OF IMMUNOLOGY 1982. [DOI: 10.4049/jimmunol.129.6.2796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
We propose a stochastic model to explain kinetic data on the delivery of lethal hits by cytotoxic T lymphocytes in multicellular conjugates. The comparison of our model with data of Zagury et al. suggests that cytotoxic T cells deliver lethal hits at random, and when conjugated to multiple target cels these cells attack undamaged target cells one at a time. The mean rate at which lethal hits are delivered per target cell is approximately the same for conjugates containing one or two target cells but slows substantially in conjugates containing three target cells. If our model is modified so that both previously hit and unhit target cells are susceptible to being lethally hit at the same rate, a very poor fit to Zagury et al's data is obtained. This leads us to conclude that previously hit cells are either not hit again or are hit at a substantially reduced rate.
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481
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Perelson AS, Bell GI. Delivery of lethal hits by cytotoxic T lymphocytes in multicellular conjugates occurs sequentially but at random times. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 1982; 129:2796-801. [PMID: 6982942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
We propose a stochastic model to explain kinetic data on the delivery of lethal hits by cytotoxic T lymphocytes in multicellular conjugates. The comparison of our model with data of Zagury et al. suggests that cytotoxic T cells deliver lethal hits at random, and when conjugated to multiple target cels these cells attack undamaged target cells one at a time. The mean rate at which lethal hits are delivered per target cell is approximately the same for conjugates containing one or two target cells but slows substantially in conjugates containing three target cells. If our model is modified so that both previously hit and unhit target cells are susceptible to being lethally hit at the same rate, a very poor fit to Zagury et al's data is obtained. This leads us to conclude that previously hit cells are either not hit again or are hit at a substantially reduced rate.
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482
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Capo C, Garrouste F, Benoliel AM, Bongrand P, Ryter A, Bell GI. Concanavalin-A-mediated thymocyte agglutination: a model for a quantitative study of cell adhesion. J Cell Sci 1982; 56:21-48. [PMID: 7166565 DOI: 10.1242/jcs.56.1.21] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
This report describes a quantitative study of the agglutination of rat thymocytes with concanavalin A (ConA). The probability that two ConA-coated cells remain bound after centrifugation was determined over a wide range of lectin concentrations. The minimal force required to separate agglutinated cells and the number of ConA molecules bound per cell were measured in similar experimental conditions. Agglutinated cells were examined by electron microscopy to estimate the area of membrane involved in adhesion. The dependence of agglutination on cell metabolism was studied: cold (4 degrees C), sodium azide (15 mM) and cytochalasin B (10 micrograms/ml) inhibited thymocyte adhesion. The importance of lateral movements of ConA molecules was assayed by measuring the adhesion of ConA-coated glutaraldehyde-fixed thymocytes to untreated cells: substantial binding occurred, but at a reduced level relative to untreated cells. A mathematical analysis of experimental data allowed the following conclusions. (1) At least 10(3) ConA bonds were involved in cross-linking two bound cells, which required the lectin molecules to be concentrated in the binding area, at least when low ConA concentrations (0.5 microgram/ml or less) were used. (2) The dependence of the binding probability on lectin concentration was fairly linear when the latter was small, which implied that the limiting step in cell-cell adhesion was the formation of a bond between a single ConA molecule and a ligand on the other cell. (3) The mean intercellular-contact time for the formation of this first bond was about 10 S for high concentrations of ligand (8 micrograms/ml). It was possible to fit the above data into a physically consistent quantitative model of cell adhesion.
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483
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Bell GI, Selby MJ, Rutter WJ. The highly polymorphic region near the human insulin gene is composed of simple tandemly repeating sequences. Nature 1982; 295:31-5. [PMID: 7035959 DOI: 10.1038/295031a0] [Citation(s) in RCA: 387] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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484
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Bell GI, Karam JH, Rutter WJ. Polymorphic DNA region adjacent to the 5' end of the human insulin gene. Proc Natl Acad Sci U S A 1981; 78:5759-63. [PMID: 6272317 PMCID: PMC348853 DOI: 10.1073/pnas.78.9.5759] [Citation(s) in RCA: 640] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The length of a segment of DNA associated with the human insulin gene, which has been localized to the short arm of chromosome 11, is heterozygous in 63% of 52 individuals analyzed. This polymorphic region is approximately 500 base pairs from the nucleotide encoding the 5' end of insulin mRNA. The polymorphism appears to be due to an insertion or deletion of DNA sequences so that DNA fragments of different length are generated when DNA from a heterozygous individual is digested with selected restriction endonucleases.
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485
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Bell GI. Estimate of the sticking probability for cells in uniform shear flow with adhesion caused by specific bonds. CELL BIOPHYSICS 1981; 3:289-304. [PMID: 6170445 DOI: 10.1007/bf02782629] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
A theory is developed for the aggregation rate of cells in uniform shear flow when the cell-cell adhesion is mediated by bonds between specific molecules on the cell surfaces such as antigen and antibody or lectin and carbohydrate. The theory is based on estimates of the frequency and duration of cell-cell collisions and of the number of bonds formed and required to hold the cells together. For high shear rates, the sticking probability is a function of a single dimensionless parameter, A, that is proportional to G-2, with G the shear rate. For low shear rates, the sticking probability is a function of a second dimensionless parameter, A' proportional to G-1. In either case the rate of cell-cell sticking is a maximum when A (or A') congruent to 1.0. For small values of A (or A') the cells collide frequently, but do not stick, whereas for large values of A (or A') the cells collide infrequently, but stick with larger probability. Studies in Couette viscometer or other flow having approximately uniform shear can test these models.
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486
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Bull P, Campino C, Bell GI, Venegas A, Valenzuela P. The effect of pH on the structure and activity of yeast RNA polymerase I. Arch Biochem Biophys 1981; 209:637-42. [PMID: 7027960 DOI: 10.1016/0003-9861(81)90323-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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487
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Owerbach D, Bell GI, Rutter WJ, Brown JA, Shows TB. The insulin gene is located on the short arm of chromosome 11 in humans. Diabetes 1981; 30:267-70. [PMID: 7009275 DOI: 10.2337/diab.30.3.267] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The human insulin gene has been previously localized to chromosome 11. We have analyzed the human DNA sequences present in a human-mouse somatic cell hybrid line possessing a translocation involving human chromosomes 11 and X. These data indicate that the human insulin gene is located on the short arm of chromosome 11 in the region p13 leads to pter.
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488
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Bell GI, Pictet R, Rutter WJ. Analysis of the regions flanking the human insulin gene and sequence of an Alu family member. Nucleic Acids Res 1980; 8:4091-109. [PMID: 6253909 PMCID: PMC324221 DOI: 10.1093/nar/8.18.4091] [Citation(s) in RCA: 133] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The regions around the human insulin gene have been studied by heteroduplex, hybridization and sequence analysis. These studies indicated that there is a region of heterogeneous length located approximately 700 bp before the 5' end of the gene; and that the 19 kb of cloned DNA which includes the 1430 bp insulin gene as well as 5650 bp before and 11,500 bp after the gene is single copy sequence except for 500 bp located 6000 bp from the 3' end of the gene. This 500 bp segment contains a member of the Alu family of dispersed middle repetitive sequences as well as another less highly repeated homopolymeric segment. The sequence of this region was determined. This Alu repeat is bordered by 19 bp direct repeats and also contains an 83 bp sequence which is present twice. The regions flanking the human and rat I insulin genes were compared by heteroduplex analysis to localize homologous sequences in the flanking regions which could be involved in the regulation of insulin biosynthesis. The homology between the two genes is restricted to the region encoding preproinsulin and a short region of approximately 60 bp flanking the 5' side of the genes.
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489
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Owerbach D, Bell GI, Rutter WJ, Shows TB. The insulin gene is located on chromosome 11 in humans. Nature 1980; 286:82-4. [PMID: 6248796 DOI: 10.1038/286082a0] [Citation(s) in RCA: 75] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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490
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Bell GI, Pictet RL, Rutter WJ, Cordell B, Tischer E, Goodman HM. Sequence of the human insulin gene. Nature 1980; 284:26-32. [PMID: 6243748 DOI: 10.1038/284026a0] [Citation(s) in RCA: 410] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The human insulin gene contains two intervening sequences, one is within the region transcribed into the 5'-untranslated segment of the mRNA and the other interrupts the C-peptide encoding region. A comparison of the human with the rat insulin genes indicates potential regulatory regions in the DNA segment preceding the gene and suggests that the ancestral form of the insulin gene had two intervening sequences.
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491
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Bell GI, Swain WF, Pictet R, Cordell B, Goodman HM, Rutter WJ. Nucleotide sequence of a cDNA clone encoding human preproinsulin. Nature 1979; 282:525-7. [PMID: 503234 DOI: 10.1038/282525a0] [Citation(s) in RCA: 117] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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492
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Bell GI. A theoretical model for adhesion between cells mediated by multivalent ligands. CELL BIOPHYSICS 1979; 1:133-47. [PMID: 95173 DOI: 10.1007/bf02781347] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A theoretical model is developed for cell-to-cell binding by bivalent ligands that can bind to mobile receptors on the cell surfaces. Monovalent inhibitors that can bind either to receptors or ligands are also included. For symmetrical ligands, that is, ligands in which both binding sites are the same, it is shown that crosslinking of receptors on each cell will interfere with intercellular bridge formation. At equilibrium, such interference is not drastic, but if the crosslinks can form before the cells are brought into contact, crosslinking may greatly impede the rate of intercellular binding. Comparison is made with experiments, and the importance of receptor mobility is discussed. It is noted that ligands can also bind a cell to itself or to a surface.
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493
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Tekamp PA, Valenzuela P, Maynard T, Bell GI, Rutter WJ. Specific gene transcription in yeast nuclei and chromatin by added homologous RNA polymerases I and II. J Biol Chem 1979; 254:955-63. [PMID: 368064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
When treated at pH less than 4.5, yeast nuclei or chromatin lose endogenous RNA synthetic activity. This activity is regained by addition of exogenous RNA polymerases. The specificity of transcription in this system by homologous RNA polymerases I and III has been investigated by gel electrophoresis, hybridization analysis, and RNase T1 mapping. Exogenous RNA polymerase I selectively transcribes rRNA genes. The transcription of these genes by polymerase I is 30- and 8-fold more selective than RNA polymerase III and Escherichia coli polymerase holoenzyme, respectively. Exogenous RNA polymerase III synthesized RNAs similar in size to authentic 5 S RNA, 4.5 S pre-tRNA, and 4 S tRNA. Eleven per cent of this RNA is 5 S RNA as determined by hybridization. Neither polymerase I nor E. coli polymerase synthesizes detectable quantities of RNA in this size range. AT1 ribonuclease digestion of 5 S RNA synthesized by exogenous RNA polymerase III acting on acid-treated chromatin gives a fragment pattern corresponding to that of 5 S RNA. Thus, RNA polymerase III transcribes the entire 5 S gene in this system.
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494
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Abstract
A theoretical framework is proposed for the analysis of adhesion between cells or of cells to surfaces when the adhesion is mediated by reversible bonds between specific molecules such as antigen and antibody, lectin and carbohydrate, or enzyme and substrate. From a knowledge of the reaction rates for reactants in solution and of their diffusion constants both in solution and on membranes, it is possible to estimate reaction rates for membrane-bound reactants. Two models are developed for predicting the rate of bond formation between cells and are compared with experiments. The force required to separate two cells is shown to be greater than the expected electrical forces between cells, and of the same order of magnitude as the forces required to pull gangliosides and perhaps some integral membrane proteins out of the cell membrane.
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495
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Valenzuela P, Bell GI, Weinberg F, Rutter WJ. Isolation and assay of eukaryotic DNA-dependent RNA polymerases. Methods Cell Biol 1978; 19:1-26. [PMID: 357912 DOI: 10.1016/s0091-679x(08)60006-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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496
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Bell GI, DeGennaro LJ, Gelfand DH, Bishop RJ, Valenzuela P, Rutter WJ. Ribosomal RNA genes of Saccharomyces cerevisiae. I. Physical map of the repeating unit and location of the regions coding for 5 S, 5.8 S, 18 S, and 25 S ribosomal RNAs. J Biol Chem 1977; 252:8118-25. [PMID: 334774] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The organization of the ribosomal DNA repeating unit from Saccharomyces cerevisiae has been analyzed. A cloned ribosomal DNA repeating unit has been mapped with the restriction enzymes Xma 1, Kpn 1, HindIII, Xba 1, Bgl I + II, and EcoRI. The locations of the sequences which code for 5 S, 5.8 S, 18 S, and 25 S ribosomal RNAs have been determined by hybridization of the purified RNA species with restriction endonuclease generated fragments of the repeating unit. The position of the 5.8 S ribosomal DNA sequences within the repeat was also established by sequencing the DNA which codes for 83 nucleotides at the 5' end of 5.8 S ribosomal RNA. The polarity of the 35 S ribosomal RNA precursor has been established by a combination of hybridization analysis and DNA sequence determination and is 5'-18 S, 5.8 S, 25 S-3'.
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497
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Valenzuela P, Bell GI, Venegas A, Sewell ET, Masiarz FR, DeGennaro LJ, Weinberg F, Rutter WJ. Ribosomal RNA genes of Saccharomyces cerevisiae. II. Physical map and nucleotide sequence of the 5 S ribosomal RNA gene and adjacent intergenic regions. J Biol Chem 1977; 252:8126-35. [PMID: 334775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
A DNA fragment containing the structural gene for the 5 S ribosomal RNA and intergenic regions before and after the 35 S ribosomal RNA precursor gene of Saccharomyces cerevisiae has been amplified in a bacterial plasmid and physically mapped by restriction endonuclease cleavage and hybridization to purified yeast 5 S ribosomal RNA. The nucleotide sequence of the DNA fragments carrying the 5 S ribosomal RNA gene and adjacent regions has been determined. The sequence unambiguously identifies the 5 S ribosomal RNA gene, determines its polarity within the ribosomal DNA repeating unit, and reveals the structure of its promoter and termination regions. Partial DNA sequence of the regions near the beginning and end of the 35 S ribosomal RNA gene has also been determined as a preliminary step in establishing the structure of promoter and termination regions for the 35 S ribosomal RNA gene.
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498
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Valenzuela P, Bell GI, Masiarz FR, DeGennaro LJ, Rutter WJ. Nucleotide sequence of the yeast 5S ribosomal RNA gene and adjacent putative control regions. Nature 1977; 267:641-3. [PMID: 327335 DOI: 10.1038/267641a0] [Citation(s) in RCA: 70] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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499
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Bell GI, Valenzuela P, Rutter WJ. Phosphorylation of yeast DNA-dependent RNA polymerases in vivo and in vitro. Isolation of enzymes and identification of phosphorylated subunits. J Biol Chem 1977; 252:3082-91. [PMID: 323261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Yeast DNA-dependent RNA polymerases I, II, and III are phosphorylated in vivo. Yeast cells were grown continuously in 32Pi and the RNA polymerases were isolated by a new procedure which allows the simultaneous purification of these enzymes from small quantities (35 to 60 g) of cells. Each of the RNA polymerases was phosphorylated. The following phosphorylated polymerase polypeptides were identified: polymerase I subunits of 185,000, 44,000, 36,000, 24,000, and 20,000 daltons; a polymerase II subunit of 24,000 daltons; and polymerase III subunits of 24,000 and 20,000 daltons. The incorporated 32P was acid-stable but base-labile. Phosphoserine and phosphothreonine were identified after partial acid hydrolysis of purified [32P]polymerase I. A yeast protein kinase that co-purifies with polymerase I during part of the isolation procedure was partially purified and characterized. This protein kinase phosphorylates the subunits of the purified polymerases that are phosphorylated in vivo and, in addition, a polymerase I subunit of 48,000 daltons and a polymerase II subunit of 33,500 daltons. Phosphorylation of the purified enzymes with this protein kinase had no substantial effect on polymerase activity in simple assays using native yeast DNA as a template. Preincubation of purified polymerase I with acid or alkaline phosphatase also had no detectable effect on polymerase activity.
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500
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Perelson AS, Bell GI. Mathematical models for the evolution of multigene families by unequal crossing over. Nature 1977; 265:304-10. [PMID: 834278 DOI: 10.1038/265304a0] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Mathematical models of homologous but unequal crossing over between sister chromatids are presented. For mispairing by one repeat, the evolution of a multigene family by unequal crossing over can be represented by a linear birth-death process. The fixation rate of one repeat in a multigene family is estimated. For mispairing by more than one repeat, some approximate results are obtained.
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