Localization of curved DNA and its association with nucleosome phasing in the promoter region of the human estrogen receptor alpha gene.
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We determined DNA bend sites in the promoter region of the human estrogen receptor (ER) gene by the circular permutation assay. A total of five sites (ERB-4 to -1, and ERB+1) mapped in the 3 kb region showed an average distance of 688 bp. Most of the sites were accompanied by short poly(dA) x poly(dT) tracts including the potential bend core sequence A2N8A2N8A2 (A/A/A). Fine mapping of the ERB-2 site indicated that this A/A/A and the 20 bp immediate flanking sequence containing one half of the estrogen response element were the sites of DNA curvature. All of the experimentally mapped bend sites corresponded to the positions of DNA curvature as well as to nucleosomes predicted by computer analysis. In vitro nucleosome mapping at ERB-2 revealed that the bend center was located 10-30 bp from the experimental and predicted nucleosome dyad axes. (+info)
Transposition of the autonomous Fot1 element in the filamentous fungus Fusarium oxysporum.
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Autonomous mobility of different copies of the Fot1 element was determined for several strains of the fungal plant pathogen Fusarium oxysporum to develop a transposon tagging system. Two Fot1 copies inserted into the third intron of the nitrate reductase structural gene (niaD) were separately introduced into two genetic backgrounds devoid of endogenous Fot1 elements. Mobility of these copies was observed through a phenotypic assay for excision based on the restoration of nitrate reductase activity. Inactivation of the Fot1 transposase open reading frame (frameshift, deletion, or disruption) prevented excision in strains free of Fot1 elements. Molecular analysis of the Nia+ revertant strains showed that the Fot1 element reintegrated frequently into new genomic sites after excision and that it can transpose from the introduced niaD gene into a different chromosome. Sequence analysis of several Fot1 excision sites revealed the so-called footprint left by this transposable element. Three reinserted Fot1 elements were cloned and the DNA sequences flanking the transposon were determined using inverse polymerase chain reaction. In all cases, the transposon was inserted into a TA dinucleotide and created the characteristic TA target site duplication. The availability of autonomous Fot1 copies will now permit the development of an efficient two-component transposon tagging system comprising a trans-activator element supplying transposase and a cis-responsive marked element. (+info)
Mechanisms of double-strand-break repair during gene targeting in mammalian cells.
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In the present study, the mechanism of double-strand-break (DSB) repair during gene targeting at the chromosomal immunoglobulin mu-locus in a murine hybridoma was examined. The gene-targeting assay utilized specially designed insertion vectors genetically marked in the region of homology to the chromosomal mu-locus by six diagnostic restriction enzyme site markers. The restriction enzyme markers permitted the contribution of vector-borne and chromosomal mu-sequences in the recombinant product to be determined. The use of the insertion vectors in conjunction with a plating procedure in which individual integrative homologous recombination events were retained for analysis revealed several important features about the mammalian DSB repair process:The presence of the markers within the region of shared homology did not affect the efficiency of gene targeting. In the majority of recombinants, the vector-borne marker proximal to the DSB was absent, being replaced with the corresponding chromosomal restriction enzyme site. This result is consistent with either formation and repair of a vector-borne gap or an "end" bias in mismatch repair of heteroduplex DNA (hDNA) that favored the chromosomal sequence. Formation of hDNA was frequently associated with gene targeting and, in most cases, began approximately 645 bp from the DSB and could encompass a distance of at least 1469 bp. The hDNA was efficiently repaired prior to DNA replication. The repair of adjacent mismatches in hDNA occurred predominantly on the same strand, suggesting the involvement of a long-patch repair mechanism. (+info)
Ataxia, ocular telangiectasia, chromosome instability, and Langerhans cell histiocytosis in a patient with an unknown breakage syndrome.
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An 8 year old boy who had Langerhans cell histiocytosis when he was 15 months old showed psychomotor regression from the age of 2 years. Microcephaly, severe growth deficiency, and ocular telangiectasia were also evident. Magnetic nuclear resonance imaging showed cerebellar atrophy. Alphafetoprotein was increased. Chromosome instability after x irradiation and rearrangements involving chromosome 7 were found. Molecular study failed to show mutations involving the ataxia-telangiectasia gene. This patient has a clinical picture which is difficult to relate to a known breakage syndrome. Also, the relationship between the clinical phenotype and histiocytosis is unclear. (+info)
A restriction endonuclease from Staphylococcus aureus.
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A specific endonuclease, Sau 3AI, has been partially purified from Staphylococcus aureus strain 3A by DEAE-cellulose chromatography. The enzyme cleaves adenovirus type 5 DNA many times, SV40 DNA eight times but does not cleave double-stranded phi X174 DNA. It recognizes the sequence (see article) and cleaves as indicated by the arrows. Evidence is presented that this enzyme plays a role in the biological restriction-modification system of Staphylococcus aureus strain 3A. (+info)
Bacillus subtilis bacteriophages SP82, SPO1, and phie: a comparison of DNAs and of peptides synthesized during infection.
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The genomes of Bacillus subtilis phages phie, SPO1, and SP82 were compared by DNA-DNA hybridization, analysis of DNA fragments produced by digestion with restriction endonucleases, comparison of the arrays of peptides synthesized during infection, and phage neutralization. DNA-DNA hybridization experiments indicated that about 78% of the SP82 DNA was homologous with SPO1 DNA, whereas 40% of the phie DNA was homologous to either SPO1 or SP82 DNA. Agarose gel electrophoresis was used to compare the molecular weights of DNA fragments produced by cleavage of SP82, SPO1, and phie DNAs with the restriction endonucleases Hae III, Sal I, Hpa II, and Hha I. Digestion of the DNAs with Hae III and Sal I produced only a few fragments, whereas digestion with Hpa II and Hha I yielded 29 to 40 fragments, depending on the DNA and the enzyme. Comparing the Hpa II fragments, 51% of the SP82 fragments had mobilities which matched those of SPO1 fragments, 32% of the SP82 fragments matched the phie fragments, and 34% of the SPO1 fragments matched the phie fragments. Comparing the Hha I digestion products, 62% of the SP82 fragments had mobilities matching the SPO1 fragments, 24% of the SP82 fragments matched the phie fragments, and 22% of the SPO1 fragments matched the phie fragments. Analysis of peptides by electrophoresis on one-dimensional sodium dodecyl sulfate-polyacrylamide slab gels showed that approximately 70 phage-specific peptides were synthesized in the first 24 min of each infection. With mobility and the intervals of synthesis as criteria, 66% of the different SP82 peptides matched the SPO1 peptides, 34% of the SP82 peptides matched the phie peptides, and 37% of the SPO1 peptides matched the phie peptides. Phage neutralization assays using antiserum to SP82 yielded K values of 510 for SP82, 240 for SPO1, and 120 for phie. (+info)
Correlated genetic and EcoRI cleavage map of Bacillus subtilis bacteriophage phi105 DNA.
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The seven previously identified EcoRI cleavage fragments of phi 105 DNA were ordered with respect to their sites of origin on the phage genome by marker rescue. One fragment, H, did not carry any determinants essential for replication. This fragment was totally missing in a deletion mutant which exhibited a lysogenization-defective phenotype. There is a nonessential region on the phi 105 genome which begins in fragment B, spans fragment H, and ends in fragment F. The size of the nonessential region, as estimated by alterations observed in the fragmentation patterns of deletion mutant DNAs, is approximately 2.7 X 10(6) daltons. Two new EcoRI cleavage fragments with molecular weights of approximately 0.2 X 10(6) were detected by autoradiography of 32P-labeled DNA. These small fragments were not located on the cleavage map. (+info)
Restriction endonuclease mapping of bacteriophage phi105 and closely related temperate Bacillus subtilis bacteriophages rho10 and rho14.
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Cleavage maps of the three similar Bacillus subtilis temperate bacteriophages, phi105, rho10, and rho14, were constructed by partial digestion analysis utilizing the restriction endonuclease EcoRI. Comparison of the topography of these maps indicates that all phage DNAs posses cohesive ends and a number of EcoRI restriction sites; the fragments are conserved, and the estimated base substitution/nucleotide divergence between these phages is 0.03 to 0.07 based on conserved fragments or between 0.03 and 0.11 based on conserved cleavage sites. These lines of evidence indicate that phi105, rho10, and rho14 are closely related. Double-enzyme digestion analysis reveals that rho14 DNA has unique SalGI and BglII restriction sites and phi105 DNA has a unique SalGI restriction site, making these phages possible cloning vectors for B. subtilis. (+info)