Biology subjects

Ly, E.

Publications and source records attributed to Ly, E..

4 recordsLinked to original sources

bioRxiv2022

Global Phylogeny of the Brassicaceae Provides Important Insights into Gene Discordance

The mustard family (Brassicaceae) is a scientifically and economically important family, containing the model plant Arabidopsis thaliana and numerous crop species that feed billions worldwide. Despite its relevance, most published family phylogenies are incompletely sampled, generally contain massive polytomies, and/or show incongruent topologies between datasets. Here, we present the most complete Brassicaceae genus-level family phylogenies to date (Brassicaceae Tree of Life, or BrassiToL) based on nuclear (>1,000 genes, almost all 349 genera and 53 tribes) and plastome (60 genes, 79% of the genera, all tribes) data. We found cytonuclear discordance between nuclear and plastome-derived phylogenies, which is likely a result of rampant hybridisation among closely and more distantly related species, and highlight rogue taxa. To evaluate the impact of this rampant hybridisation on the nuclear phylogeny reconstruction, we performed four different sampling routines that increasingly removed variable data and likely paralogs. Our resulting cleaned subset of 297 nuclear genes revealed high support for the tribes, while support for the main lineages remained relatively low. Calibration based on the 20 most clock-like nuclear genes suggests a late Eocene to late Oligocene icehouse origin of the family. Finally, we propose five new or re-established tribes, including the recognition of Arabidopsideae, a monotypic tribe to accommodate Arabidopsis. With a worldwide community of thousands of researchers working on this family, our new, densely sampled family phylogeny will be an indispensable tool to further highlight Brassicaceae as an excellent model family for studies on biodiversity and plant biology.

evolutionary biology↗

bioRxiv2022

p53 binds more dynamically to response elements that are closer to the consensus sequence

The transcriptional activator p53 is a tumor suppressor protein that controls cellular pathways important for cell fate decisions, including cell cycle arrest, senescence, and apoptosis. It functions as a tetramer by binding to specific DNA sequences known as response elements (REs) to control transcription via interactions with co-regulatory complexes. Critical for understanding how p53 regulates gene expression is unraveling the fundamental mechanisms by which it binds to REs. Toward this goal we have used an in vitro single molecule fluorescence approach to quantify the dynamic binding of tetrameric p53 to five native REs in real time under equilibrium conditions. We found little evidence of dimer/DNA complexes as intermediates to the formation or dissociation of p53 tetramer/DNA complexes; however, tetramer/DNA complexes can exchange dimers at some REs. Determining rate constants for association and dissociation revealed two kinetically distinguishable populations of tetrameric p53/RE complexes. For the less stable population, the rate constants for dissociation were larger at REs closest to consensus, showing the more favorable binding sequences form the least kinetically stable complexes. Together our real time measurements provide insight into mechanisms with which tetrameric p53 forms complexes on different native REs.

biochemistry↗

bioRxiv2019

Release of human TFIIB from actively transcribing complexes is triggered upon synthesis of 7 nt and 9 nt RNAs

RNA polymerase II (Pol II) and its general transcription factors assemble on the promoters of mRNA genes to form large macromolecular complexes that initiate transcription in a regulated manner. During early transcription these complexes undergo dynamic rearrangement and disassembly as Pol II moves away from the start site of transcription and transitions into elongation. One step in disassembly is the release of the general transcription factor TFIIB, although the mechanism of release and its relationship to the activity of transcribing Pol II is not understood. We developed a single molecule fluorescence transcription system to investigate TFIIB release in vitro. Leveraging our ability to distinguish active from inactive complexes, we found that nearly all transcriptionally active complexes release TFIIB during early transcription. Release is not dependent on the contacts TFIIB makes with its recognition element in promoter DNA. We identified two different points in early transcription at which release is triggered, reflecting heterogeneity across the population of actively transcribing complexes. TFIIB releases after both trigger points with similar kinetics, suggesting the rate of release is independent of the molecular transformations that prompt release. Together our data support the model that TFIIB release is important to maintain the transcriptional activity of Pol II as initiating complexes transition into elongation complexes.

biochemistry↗

bioRxiv2019

Single molecule studies reveal that p53 tetramers dynamically bind response elements containing one or two half sites

The tumor suppressor protein p53 is at the nexus of cell fate decisions, including apoptosis, senescence, and cell cycle arrest. p53 is a tetrameric transcription factor that binds to DNA response elements to regulate transcription of its target genes, a process activated by cellular stress. p53 response elements consist of two decameric half-sites, and most data suggest one p53 dimer in the tetramer binds to each half-site. Despite a broad literature describing p53 binding to DNA, unanswered questions remain, due in part to the need for more quantitative and structural studies with the full length protein. Here we describe a single molecule fluorescence system to visualize full length p53 tetramers binding to DNA in real time. The data reveal a dynamic interaction with many p53 binding and dissociation events occurring on single DNA molecules over minutes. We found that p53 tetramers bound to response elements containing only a single half site. The kinetic stability of tetramer/DNA complexes depended on the number of half sites and the helical phasing between them, with the most stable complexes forming on DNA containing two adjacent half sites. The forward rate of binding was not strongly impacted when one half site was mutated. These studies provide real time kinetic measurements of full length p53 tetramers binding to single molecules of DNA, and reveal new insight into the mechanisms by which this nucleoprotein complex forms.

biochemistry↗