Single-molecule Studies of Eukaryotic and Prokaryotic Transcription PDF Download
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Author: Furqan Muhammad Fazal
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Languages : en
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Author: Furqan Muhammad Fazal
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Languages : en
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Author: Jing Zhou
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Languages : en
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Transcription, the process of copying genetic information stored in DNA into RNA, is fundamental to life. It is carried out by an extraordinary nano-machine called RNA polymerase (RNAP). Transcriptional elongation, during which RNAP moves along the DNA, adding one nucleotide at a time to the RNA transcript, is highly dynamic and regulated. The motion of RNAP is discontinuous and interrupted by pauses that play an essential role in gene regulation. Fundamental questions regarding the mechanisms of elongation and its modulation by transcription factors, however, remain unclear. In this dissertation, I focus on using high-resolution, optical trapping techniques to study the mechanisms of transcriptional elongation by both prokaryotic and eukaryotic RNA polymerases at the single-molecule level. First, I describe the studies on how the motion of single E.coli RNAP molecules is modulated by two universally conserved, essential transcription factors (NusA and NusG). From individual transcriptional elongation records, the rates of entering pause states, the pause state lifetimes, and the pause-free elongation speeds can all be extracted. By studying the effects of NusA (and NusG) on these kinetic rates as a function of the applied load, we were able to develop a quantitative kinetic scheme for elongation and pausing. This model not only explains the functions of NusA/NusG, but also provides insight into the mechanism of transcriptional pausing, which had previously been controversial. Second, a novel optical-trapping assay capable of directly probing elongation by individual eukaryotic RNA polymerase II (RNAPII) molecules will be described. We find that the RNAPII trigger loop, an evolutionarily conserved protein subdomain, not only affects each of the three main phases of elongation, namely: substrate binding, translocation, and catalysis; but also plays a critical role in controlling the fidelity of transcription. Our data also support a Brownian ratchet model for elongation which incorporates a secondary nucleotide binding site.
Author: Yara Xochitl Mejia
Publisher:
ISBN:
Category :
Languages : en
Pages : 282
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The present dissertation uses Optical Tweezers to examine the inner workings of one of the most relevant molecular motors in the cell: RNA polymerase. E. coli RNA polymerase has been studied for almost half a century, but fundamental questions about its translocation mechanism along DNA, as well as its pausing and stalling behavior still remain. Due to RNAP's heterogeneous behavior, a single molecule approach presents unique advantages. As part of this work, single molecule transcription experiments were done at temperatures between 7°C and 45°C. Within this temperature range, the pause-free velocity of RNAP increases with temperature with an activation energy of 9.7 ± 0.7 kcal/mole. Moreover, temperature affects pause entry and the stalling force, but not pause duration. This dissertation also presents the first single molecule study of Trigger Loop (TL) mutants, a domain thought to have a crucial role in enzyme catalysis. Our results identify TL folding as a rate-determining step in elongation and correlate TL helix propensity with pause-free velocity. Based on the inverse relation between pause-free velocity and pause entry for the mutant and wildtype polymerases and for transcription with nucleotide analogs, a quantitative kinetic model was constructed. An analysis of pause durations indicated that the TL has no role in pause recovery. Furthermore, a novel single molecule assay was developed to study RNAP's rotation velocity during elongation and in response to torsional load. Here, the DNA is stretched between two beads, and a "rotor bead" of different sizes is attached to the rotating polymerase. The pause-free angular speed is seen to decrease for increasing rotational loads corresponding to a constant torque value of 7 pNnm. Further analysis demonstrates that RNAP acts as a Brownian Ratchet and exerts an average energy per step of 1 KBT. Rotational load does not, however, have an effect on pause entry or duration. Finally, I describe a novel technique for modifying the twist of DNA. This Hybrid Tweezers technique was used for the formation of DNA plectonemes and braids, as well as for studying transcription under Torque. Together, these experiments have constructed a clearer picture of the kinetics, energetics and mechanisms of RNAP.
Author: Donald P. Nierlich
Publisher: Elsevier
ISBN: 1483273938
Category : Science
Languages : en
Pages : 668
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Molecular Mechanisms in the Control of Gene Expression documents the proceedings of the ICN-UCLA conference on Molecular Mechanisms in the Control of Gene Expression, organized through the Molecular Biology Institute of UCLA, held in Keystone, Colorado, 21-26 March 1976. The conference focused on three topics: the action of repressors on specific nucleotide sequences in DNA; how DNA and histones are intertwined in eucaryotic chromosomes; and in the development of new techniques that appear to lift genes from complex genomes. The volume contains 65 chapters organized into nine parts. The papers in Part I examine the organization of prokaryotic and eukaryotic chromosomes. Part II presents studies on the interaction of RNA a polymerase and regulatory molecules with defined DNA sites. Parts III and IV focus on RNA polymerases of eukaryotes and the regulation of transcription in eukaryotic systems, respectively. Part V contains papers dealing with nucleic acid sequences, transcription, and processing. Part VI covers cellular aspects in the study of gene expression. Part VII takes up cloning while Part VIII is devoted to genetic analysis through restriction mapping and molecular cloning. Finally, Part IX summarizes the recent progress reported at the conference and also indicates some of the limitations that can be placed upon interpretation of data.
Author: Achim P. Popp
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Languages : en
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Author: Matthew Herbert Larson
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Languages : en
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Transcription by RNAP is highly regulated in both prokaryotic and eukaryotic cells, and the ability of the cell to differentiate and respond to its environment is largely due to this regulation. During elongation, for example, RNAP is known to momentarily halt in response to certain cellular signals, and this pause state has been implicated in the regulation of gene expression in both prokaryotic and eukaryotic organisms. In addition, once RNAP reaches the end of a gene, it must reliably terminate and release the newly-transcribed RNA, providing another potential point of regulation within different cell types. Both of these steps are crucial to ensure proper gene expression. In this dissertation, I focus on transcription elongation by both prokaryotic and eukaryotic RNA polymerases, as well as their regulation through pausing and termination. To probe the role of RNA hairpins in transcriptional pausing, a novel single-molecule "RNA-pulling" assay was used to block the formation of secondary structure in the nascent transcript. Force along the RNA did not significantly affect transcription elongation rates, pause frequencies, or pause lifetimes, indicating that short "ubiquitous" pauses are not a consequence of RNA hairpins. Force-based single-molecule techniques were also used to study the mechanism and energetics of transcription termination in bacteria. The data suggest two separate mechanisms for termination: one that involves hypertranslocation of RNAP along the DNA, and one that involves shearing of the RNA:DNA hybrid within the enzyme. In addition, a quantitative energetic model is presented that successfully predicts the termination efficiency of both wild-type and mutant terminators. Finally, the implementation of a novel optical-trapping assay capable of directly observing transcription by eukaryotic RNA polymerase II (RNAPII) molecules is described. This approach was used to probe the RNAPII nucleotide-addition cycle, as well as the role of the trigger loop (a conserved subdomain) in elongation. The results are consistent with a Brownian ratchet model of elongation which incorporates a secondary NTP binding site, and the trigger loop was found to modulate translocation, NTP binding, and catalysis, as well as substrate selection and mismatch recognition by RNAPII.
Author:
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ISBN: 9780815332183
Category : Cells
Languages : en
Pages : 0
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Author: Kevin Oliver Kramm
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Languages : en
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Author: Diego Armando Duchi Llumigusin
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Languages : en
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Author: SangYoon Chung
Publisher:
ISBN:
Category :
Languages : en
Pages : 124
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The numerous complex molecular processes occurring inside living cells are primarily carried out by proteins and other biopolymers, such as ribonucleic acids (RNA). The identity and quantity of the different proteins and RNA determine the cell's phenotype and changes in response to the environment. Therefore, the internal composition of the cell in terms of the type and concentration of proteins and RNA is tightly regulated. Gene expression is the process of using the DNA sequence information to produce these biopolymers. Transcription, the initial step in gene expression, where one strand of DNA is used as template by the enzyme RNA polymerase (RNAP) for synthesizing a complementary RNA or transcript. Since cell phenotype is mostly determined by transcription, a complex regulatory mechanism exists involving a large number of factors to control the level of transcription of a gene. Although most studies are focused on multiple cycles of either transcription or association of DNA and RNA Polymerase (RNAP) to make RNAP-Promoter open complex (RPO), single round transcription studies are crucial in elucidating the mechanism of sophisticated RNAP-DNA interactions and its kinetics in transcription. In this context, we have developed a novel in vitro quenching based single round transcription assay using single molecule detection. Using this, we could successfully dissect initiation kinetics starting from different initial transcribing stages and found that transcription initiation doesn't follow a sequential model (as commonly believed). Instead, we identified a previously uncharacterized state that is unique to initial transcribing complexes and associated with the backtracked RNAP-DNA complex. Also, we have investigated the size/concentration effects of various osmolytes and macromolecular crowding agents, which mimic the crowded cellular environment, on actively-transcribing RNAP and found enhancement in transcription kinetics by larger crowding agents at the same viscosity.
