ScienceDaily (Mar. 14, 2010) — Repair proteins appear to efficiently scan the genome for errors by jumping like fleas between DNA molecules, sliding along the strands, and perhaps pausing at suspicious spots, say researchers at the University of Pittsburgh, the University of Essex and the University of Vermont who tagged the proteins with quantum dots to watch the action unfold.
DNA tightrope: (A) YOYO labeled DNA tightopes and beads; (B) UvrA-red Qdots; (C) Schematic of UvrA-Qdot bound to DNA tightrope. (Credit: Image courtesy of Bennett Van Houten, Ph.D., University of Pittsburgh Cancer Institute)
Everyone is constantly bombarded with environmental toxins that inflict small errors in the DNA code, so a rapid repair system is essential to maintain the integrity of the sequences for proper cell function, explained senior author Bennett Van Houten, Ph.D., Richard M. Cyert Professor of Molecular Oncology and leader, molecular and cellular cancer biology program, University of Pittsburgh Cancer Institute (UPCI), and professor, Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine.
"How this system works is an important unanswered question in this field," he said. "It has to be able to identify very small mistakes in a 3-dimensional morass of gene strands. It's akin to spotting potholes on every street all over the country and getting them fixed before the next rush hour."
The researchers sought to unravel the mystery by tagging two repair proteins, called UvrA and UvrB, with quantum dots, which are semi-conductor nanocrystals that light up in different colors. They also stretched the usually clumped DNA into multiple "tightropes" to see the process more clearly.
They watched while UvrA proteins randomly jumped from one DNA molecule to the next, holding on to one spot for about seven seconds before hopping to another site. But when UvrA formed a complex with two UvrB molecules (UvrAB), a new and more efficient search technique emerged: the complex slid along the DNA tightrope for as long as 40 seconds before detaching itself and jumping to another molecule.
...
Read more here/Leia mais aqui: Science Daily
Molecular Cell
Volume 37, Issue 5, 12 March 2010, Pages 702-713Neil M. Kad1, , , Hong Wang2, 3, Guy G. Kennedy4, David M. Warshaw4 and Bennett Van Houten2, 3, ,
1 Department of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, UK
2 Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA
3 The University of Pittsburgh Cancer Institute, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
4 Department of Molecular Physiology & Biophysics, University of Vermont, Burlington, VT 05405, USA
Received 8 July 2009;
revised 14 October 2009;
accepted 23 December 2009.
Published: March 11, 2010.
Available online 11 March 2010.
Summary
How DNA repair proteins sort through a genome for damage is one of the fundamental unanswered questions in this field. To address this problem, we uniquely labeled bacterial UvrA and UvrB with differently colored quantum dots and visualized how they interacted with DNA individually or together using oblique-angle fluorescence microscopy. UvrA was observed to utilize a three-dimensional search mechanism, binding transiently to the DNA for short periods (7 s). UvrA also was observed jumping from one DNA molecule to another over 1 μm distances. Two UvrBs can bind to a UvrA dimer and collapse the search dimensionality of UvrA from three to one dimension by inducing a substantial number of UvrAB complexes to slide along the DNA. Three types of sliding motion were characterized: random diffusion, paused motion, and directed motion. This UvrB-induced change in mode of searching permits more rapid and efficient scanning of the genome for damage.
Graphical Abstract
1 Department of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, UK
2 Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA
3 The University of Pittsburgh Cancer Institute, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
4 Department of Molecular Physiology & Biophysics, University of Vermont, Burlington, VT 05405, USA
Received 8 July 2009;
revised 14 October 2009;
accepted 23 December 2009.
Published: March 11, 2010.
Available online 11 March 2010.
Summary
How DNA repair proteins sort through a genome for damage is one of the fundamental unanswered questions in this field. To address this problem, we uniquely labeled bacterial UvrA and UvrB with differently colored quantum dots and visualized how they interacted with DNA individually or together using oblique-angle fluorescence microscopy. UvrA was observed to utilize a three-dimensional search mechanism, binding transiently to the DNA for short periods (7 s). UvrA also was observed jumping from one DNA molecule to another over 1 μm distances. Two UvrBs can bind to a UvrA dimer and collapse the search dimensionality of UvrA from three to one dimension by inducing a substantial number of UvrAB complexes to slide along the DNA. Three types of sliding motion were characterized: random diffusion, paused motion, and directed motion. This UvrB-induced change in mode of searching permits more rapid and efficient scanning of the genome for damage.
Graphical Abstract
Highlights
► The NER proteins UvrA/B were quantum-dot-tagged and visualized on DNA tightropes ► UvrA binds to DNA on average for 7 s and can hop between strands up to 1 μm ► UvrB alters UvrA's search mechanism to include several forms of 1D sliding ►
Dual color imaging indicates UvrA coordinates the formation of a UvrA2B2 complex
Author Keywords: DNA
+++++
Professores, pesquisadores e alunos de universidades públicas e privadas com acesso ao site CAPES/Periódicos podem ler gratuitamente este artigo da Molecular Cell e de mais 22.440 publicações científicas.
+++++
Fui, nem sei por que, com uma baita dó de Darwin (o homem que teve a maior ideia que toda a humanidade já teve: a evolução através da seleção natural) e as limitações do seu microscópio rudimentar que nem podia ver direito o que é uma célula e toda a sua complexidade irredutível.
Mero acaso, fortuita necessidade ou 100% design inteligente???
Gente, eu me esqueci do comentário impertinente. Diz o mantra dobzhanskyano que nada em biologia faz sentido a não ser à luz da evolução. Só que os autores nos deixaram nas 'trevas', pois não explicaram evolutivamente como tudo isso evoluiu.
Fui, nem sei por que, pensando que o Dobzhansky realmente disse no Brasil: "Evidências? Que se danem as evidências, o que vale é a teoria."
► The NER proteins UvrA/B were quantum-dot-tagged and visualized on DNA tightropes ► UvrA binds to DNA on average for 7 s and can hop between strands up to 1 μm ► UvrB alters UvrA's search mechanism to include several forms of 1D sliding ►
Dual color imaging indicates UvrA coordinates the formation of a UvrA2B2 complex
Author Keywords: DNA
+++++
Professores, pesquisadores e alunos de universidades públicas e privadas com acesso ao site CAPES/Periódicos podem ler gratuitamente este artigo da Molecular Cell e de mais 22.440 publicações científicas.
+++++
Fui, nem sei por que, com uma baita dó de Darwin (o homem que teve a maior ideia que toda a humanidade já teve: a evolução através da seleção natural) e as limitações do seu microscópio rudimentar que nem podia ver direito o que é uma célula e toda a sua complexidade irredutível.
Mero acaso, fortuita necessidade ou 100% design inteligente???
Gente, eu me esqueci do comentário impertinente. Diz o mantra dobzhanskyano que nada em biologia faz sentido a não ser à luz da evolução. Só que os autores nos deixaram nas 'trevas', pois não explicaram evolutivamente como tudo isso evoluiu.
Fui, nem sei por que, pensando que o Dobzhansky realmente disse no Brasil: "Evidências? Que se danem as evidências, o que vale é a teoria."
