该发现为开发更好的以细菌转录机制为靶标的抗生素铺平了道路.
    (2010年1月13日,纽约)纽约大学兰贡医学中心的科学家在对Rho因子—大肠杆菌及其他很多细菌的关键调控蛋白—作用的研究中有了新发现.这项研究发表于2010年1月14日的《自然》期刊上,它揭示了一种关于基因转录控制的分子机制的新模式.这项工作很可能将导致新的以Rho因子及其关键功能为靶标的新型抗生素的诞生.
    1969年发现的Rho因子是细菌及其他生物中第一个被阐明的转录终止因子,它是基因转录的“红灯“,对很多种类细菌的生存起着至关重要的作用.但至今人们仍未了解Rho因子的确切工作机理.较为流行的假说是:在转录过程中,Rho因子可附着于正在合成的RNA的特定位置并沿着该RNA链移动以“追赶”RNA聚合酶,一旦追上,Rho因子就可以终止转录.但新的研究发现推翻了这种教科书里的假说,研究者提出了一种全新的关于Rho因子如何终止转录的机制.
    这项研究的作者认为以前关于Rho因子终止转录的那种“被动”模式并不正确,并为此提供了令人信服的实验证据.相反,他们提出了直接的证据证明变构机制,即RNA聚合酶的催化中心的特定构象变化,是Rho因子引起的转录中止的原因.这种新模式也为理解所有生物的转录终止的分子机制提供了总体性的思路和方法.另外,研究也表明不管是体内或体外实验,在整个转录过程中Rho因子都紧密结合于RNA聚合酶.这个令人兴奋的发现暗示Rho因子就像RNA聚合酶的亚基一样与之紧密结合,一旦RNA聚合酶所合成的未受保护的RNA链足够长,Rho因子会使RNA聚合酶转变至终止模式.
    “只要真正了解这个关键转录因子的确切工作原理,就可以设计小分子物质以改变其功能,并促使细菌无法存活,”该研究的第一作者,纽约大学兰贡医学中心的生化学教授,Evgeny Nudler博士说,“也可以利用这个新发现是细菌变得为人类所用,如改造某些菌株,使其得以大量生产某些重要的营养物质,如维他命和氨基酸等事实上,在Nudler及其同事发表于去年的《科学》杂志上的一个研究论文中,作者利用特异性作用于Rho因子的双环霉素以揭示该转录因子在细胞中的角色与功能.他们发现,通过调控所转录的RNA的量以满足细胞所需,Rho因子几乎控制着大肠杆菌中所有基因的表达.同时,作者发现Rho因子在保护细菌免受所谓“水平转运”基因(如细菌从病毒或其他细菌中摄取的基因)的毒性作用的过程中也起着关键作用,是正是这些基因中的大部分使细菌具备对抗生素的抗性.

Paradigm changing mechanism is revealed for the control of gene expression in bacteria
Findings pave the way for designing better antibiotics targeting bacterial transcription machinery
    (New York, NY, January 13, 2009) A new study led by researchers at NYU Langone Medical Center is shedding new light on the action of Rho, a key regulatory protein in E. coli and many other bacteria. The study published in the January 14, 2010 issue of Nature reveals a new paradigm to understand the molecular principles of gene transcription. This work could potentially lead to the development of new types of antibiotics that could target Rho and its crucial functions. 


    Rho – discovered in 1969 -- is the first transcription termination factor described in bacteria and other organisms. It acts as a red light to gene transcription and is essential for survival in many bacterial species. But the actual mechanism by which it works has been unknown. It was postulated that Rho loads onto RNA at a specific site and then translocates along the nascent transcript in pursuit of the moving RNA polymerase that is in the process of RNA synthesis. Once the RNA polymerase is paused, Rho has the chance to catch up and terminate transcription. In the new study researchers at the NYU Langone Medical Center challenge this textbook paradigm and provide a completely new mechanism of the Rho termination process.
    The authors provide compelling experimental evidence against previously proposed "passive" models of Rho termination. Instead, they present direct evidence for an allosteric mechanism in which specific conformational changes in RNA polymerase catalytic center are responsible for Rho termination. This model provides a general conceptual framework from which to understand the molecular principles of all termination mechanisms. In addition, the study shows that Rho binds tightly to RNA polymerase throughout the transcription cycle, both in vitro and in vivo. This striking observation implies that Rho acts like a "subunit" of RNA polymerase that switches to the termination mode as soon as a sufficiently long segment of unprotected transcript emerges from RNA polymerase onto which Rho can load.
    "Once you know the exact mechanism by which a key transcription factor works, you can design small molecules to alter its function so that bacteria won\'t be able to survive," says Evgeny Nudler, PhD, the Julie Wilson Anderson Professor of Biochemistry at NYU Langone Medical Center and lead author of the study. "You can also use this new information to alter bacteria in a positive way,that is to design bacterial strains that can produce essential nutrients like vitamins and amino acids in larger quantities."
    Indeed, in the study published by Nudler and coworkers last year in Science, the researchers used antibiotic bicyclomycin, which specifically target Rho to uncover the functional role of this termination factor in the cell. They found that Rho was responsible for controlling the expression of almost every gene in E.coli, by adjusting the overall transcriptional yield to cellular needs. Moreover, they found that Rho also plays critical role in protecting bacteria from the toxic effects of so called "horizontally transferred" genes, i.e. genes that bacteria picked up from viruses and other bacteria. Many of those genes make bacteria resistant to antibiotics.
    Co-authors of the new study include Vitaly Epshtein, PhD and Dipak Dutta, PhD, of the Department of Biochemistry at NYU Langone Medical Center, and Joseph Wade of the Department of Biomedical Sciences, School of Public Health, University at Albany


    The study was funded by a grant from the National Institutes of Health (R01GM58750) in Bethesda, Maryland.
About NYU Langone Medical Center
    NYU Langone Medical Center is one of the nation\'s premier centers of excellence in healthcare, biomedical research, and medical education. For over 168 years, NYU physicians and researchers have made countless contributions to the practice and science of health care. Today the Medical Center consists of NYU School of Medicine, including the Smilow Research Center, the Skirball Institute of Biomolecular Medicine, and the Sackler Institute of Graduate Biomedical Sciences; the three hospitals of NYU Hospitals Center, Tisch Hospital, a 705-bed acute-care general hospital, Rusk Institute of Rehabilitation Medicine, the first and largest facility of its kind, and NYU Hospital for Joint Diseases, a leader in musculoskeletal care; and such major programs as the NYU Cancer Institute, the NYU Child Study Center, and the Hassenfeld Children\'s Center for Cancer and Blood Disorders.

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