Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.31.1 (micrococcal nuclease)
 2,818 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Oxytricha macronuclear DNA exists as approximately 24 X 10(6) gene-sized molecules terminating with a C4A4 repeat. DNA-protein interactions at the ends of bulk macronuclear molecules were probed with micrococcal nuclease and methidiumpropyl-EDTA X Fe(II) (MPE X Fe[II]). The ends were indirectly labeled by hybridizing with (C4A4)2. Alternatively, a novel method using MPE X FE(II) as a probe and directly labeling the 3' ends with terminal transferase was implemented. A terminal complex involving approximately 100 bp with nucleosomes phased inward from the complex was found to be characteristic of most or all of the ends. Analysis of two specific genes confirmed the pattern and showed that the special structure was on both ends of each molecule. We conclude that a DNA-protein complex involving 100 bp and terminating with the C4A4 repeat can be sufficient to provide the fundamental functions of telomeres, allowing linear DNA replication and conferring stability of linear DNA.
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PMID:Chromatin structure of the molecular ends of Oxytricha macronuclear DNA: phased nucleosomes and a telomeric complex. 643 44

The gene A protein cleaves phi X174 single-stranded DNA (ssDNA). The cleavage appears to be stoichiometric, whereby a gene A protein molecule breaks a phosphodiester bond and binds to the 5' end. The enzyme introduces mostly a single break in a circular ssDNA molecule. However, at high enzyme-to-DNA ratios, more than one break in the DNA could be observed. The cleavage of the ssDNA by gene A protein renders the DNA sensitive to the action of terminal transferase to incorporate [alpha -32P]ATP. Thus, the 3'OH end is free. All attempts to label the 5' end by T4-induced polynucleotide kinase and [gamma-32P]ATP failed. The formation of a gene A-ssDNA complex was demonstrated directly by using 3H-labeled gene A protein and 32P-labeled ssDNA in the reaction. Such a complex is resistant to treatments with 0.2 M NaOH, banding in CsCl, and boiling in 2.5% sodium dodecyl sulfate. Only treatment with a nuclease released the bound protein. Also, after cleaving [32P]ssDNA by gene A protein, followed by either DNase I or micrococcal nuclease digestion, a fraction of the 32P label remained resistant to nuclease treatment and comigrated with gene A protein on polyacrylamide gels.
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PMID:Cleavage of phi X174 single-stranded DNA by gene A protein and formation of a tight protein-DNA complex. 644 6

Macronuclear telomeres in Oxytricha exist as DNA-protein complexes in which the termini of the G-rich strands are bound by a 97-kDa telomere protein. During telomeric DNA replication, the replication machinery must have access to the G-rich strand. However, given the stability of telomere protein binding, it has been unclear how this is accomplished. In this study we investigated the ability of several different DNA polymerases to access telomeric DNA in Oxytricha telomere protein-DNA complexes. Although DNA bound by the telomere protein is not degraded by micrococcal nuclease or labeled by terminal deoxynucleotidyltransferase, this DNA serves as an efficient primer for the addition of telomeric repeats by telomerase, a specialized RNA-dependent DNA polymerase (ribonucleoprotein reverse transcriptase), EC 2.7.7.49. Moreover, in the presence of a suitable complementary C-rich DNA template, AMV reverse transcriptase and the E. coli Klenow fragment will also elongate DNA bound by the telomere protein. These findings indicate that the 3' terminus and the Watson-Crick base pairing positions are exposed in the protein complex. We propose that the telomere protein can serve a dual role at the telomere by protecting the DNA phosphate backbone from degradation while simultaneously exposing the DNA bases for replication.
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PMID:DNA bound by the Oxytricha telomere protein is accessible to telomerase and other DNA polymerases. 750 21