Biology subjects

Becker, N. A.

Publications and source records attributed to Becker, N. A..

3 recordsLinked to original sources

bioRxiv2026

LOOP-TAG: massively-parallel measurement of length-dependent protein-mediated DNA looping probabilities by tagmentation in vitro

We are interested in DNA stiffness in vitro and in vivo. Classical approaches for measuring this parameter in vitro involve tedious T4 DNA ligase-mediated cyclization kinetics experiments performed for one DNA fragment length at a time to establish effective local end-end concentrations (J-factors). Protein-mediated DNA looping is a more relevant biological reaction. An efficient approach to determine length-dependent protein-mediated DNA J-loop values in vitro has been lacking. We describe LOOP-TAG, a massively-parallel method. We leverage intramolecular DNA looping and tagmentation catalyzed by Tn5 transposase (Tnp) tethered to the terminus of a ~1,000-bp bead-bound duplex DNA. We detected loops terminating with Tnp. Counts of the resulting DNA looping-dependent bead-bound tagmentation products from deep sequencing determine DNA loop length probabilities at single-base pair resolution for all bead-bound fragments. When normalized to DNA fragment length probabilities from tagmentation using known concentrations of free Tnp, length-dependent J-loop values are directly determined. We demonstrate LOOP-TAG for Tnp tethered in two ways and in the presence of DNA-kinking architectural DNA binding protein Nhp6A. Intermediate length J-loop values are consistent with expectations of wormlike chain theory after accounting for strong sequence-dependence of Tnp. DNA loops are shifted to smaller sizes in the presence of Nhp6A, as predicted.

biophysics↗

bioRxiv2024

Probing mechanical selection in diverse eukaryotic genomes through accurate prediction of 3D DNA mechanics

Connections between the mechanical properties of DNA and biological functions have been speculative due to the lack of methods to measure or predict DNA mechanics at scale. Recently, a proxy for DNA mechanics, cyclizability, was measured by loop-seq and enabled genome-scale investigation of DNA mechanics. Here, we use this dataset to build a computational model predicting bias-corrected intrinsic cyclizability, with near-perfect accuracy, solely based on DNA sequence. Further, the model predicts intrinsic bending direction in 3D space. Using this tool, we aimed to probe mechanical selection - that is, the evolutionary selection of DNA sequence based on its mechanical properties - in diverse circumstances. First, we found that the intrinsic bend direction of DNA sequences correlated with the observed bending in known protein-DNA complex structures, suggesting that many proteins co-evolved with their DNA partners to capture DNA in its intrinsically preferred bent conformation. We then applied our model to large-scale yeast population genetics data and showed that centromere DNA element II, whose consensus sequence is unknown, leaving its sequence-specific role unclear, is under mechanical selection to increase the stability of inner-kinetochore structure and to facilitate centromeric histone recruitment. Finally, in silico evolution under strong mechanical selection discovered hallucinated sequences with cyclizability values so extreme that they required experimental validation, yet, found in nature in the densely packed mitochondrial(mt) DNA of Namystynia karyoxenos, an ocean-dwelling protist with extreme mitochondrial gene fragmentation. The need to transmit an extraordinarily large amount of mtDNA, estimated to be > 600 Mb, in combination with the absence of mtDNA compaction proteins may have pushed mechanical selection to the extreme. Similarly extreme DNA mechanics are observed in bird microchromosomes, although the functional consequence is not yet clear. The discovery of eccentric DNA mechanics in unrelated unicellular and multicellular eukaryotes suggests that we can predict extreme natural biology which can arise through strong selection. Our methods offer a way to study the biological functions of DNA mechanics in any genome and to engineer DNA sequences with desired mechanical properties.

biophysics↗

bioRxiv2021

Designed architectural proteins that tune DNA looping in bacteria

Architectural proteins alter the shape of DNA, often by distorting the double helix and introducing sharp kinks that relieve strain in tightly-bent DNA structures. Here we design and test artificial architectural proteins based on a sequence-specific Transcription Activator-like Effector (TALE) protein, either alone or fused to a eukaryotic high mobility group B (HMGB) DNA-bending domain. We hypothesized that TALE protein binding would stiffen DNA to bending and twisting, acting as an architectural protein that antagonizes the formation of small DNA loops. In contrast, fusion to an HMGB domain was hypothesized to generate a targeted DNA-bending architectural protein that facilitates DNA looping. We provide evidence from E. coli Lac repressor gene regulatory loops supporting these hypotheses in living bacteria. Both data fitting to a thermodynamic DNA looping model and sophisticated molecular modeling support the interpretation of these results. We find that TALE protein binding inhibits looping by stiffening DNA to bending and twisting, while the Nhp6A domain enhances looping by bending DNA without introducing twisting flexibility. Our work illustrates artificial approaches to sculpt DNA geometry with functional consequences. Similar approaches may be applicable to tune the stability of small DNA loops in eukaryotes.

biochemistry↗