Protamine folds DNA into flowers and loop stacks.

DNA in sperm undergoes an extreme compaction to almost crystalline packing levels. To produce this dense packing, DNA is dramatically reorganized in minutes by protamine proteins. Protamines are positively charged proteins that coat negatively charged DNA and fold it into a series of toroids.

Patient-Specific Risk Factors Associated With the Development of Hyperchloremia in a Neurocritical Care Intensive Care Unit.

Background: Hypertonic sodium chloride (HTS) is used in intensive care unit (ICU) settings to manage cerebral edema, intracranial hypertension, and for the treatment of severe hyponatremia. It has been associated with an increased incidence of hyperchloremia; however, there is limited literature focusing on hyperchloremic risk in neurologically injured patients. Objective: The primary objective of this study was to determine risk factors associated with development of hyperchloremia in a neurocritical care (NCC) ICU population.

DNA looping by protamine follows a nonuniform spatial distribution.

DNA looping plays an important role in cells in both regulating and protecting the genome. Often, studies of looping focus on looping by prokaryotic transcription factors like lac repressor or by structural maintenance of chromosomes proteins such as condensin. Here, however, we are interested in a different looping method whereby condensing agents (charge ≥+3) such as protamine proteins neutralize the DNA, causing it to form loops and toroids.

A Surface-Coupled Optical Trap with 1-bp Precision via Active Stabilization.

Optical traps can measure bead motions with Å-scale precision. However, using this level of precision to infer 1-bp motion of molecular motors along DNA is difficult, since a variety of noise sources degrade instrumental stability. In this chapter, we detail how to improve instrumental stability by (1) minimizing laser pointing, mode, polarization, and intensity noise using an acousto-optical-modulator mediated feedback loop and (2) minimizing sample motion relative to the optical trap using a three-axis piezo-electric-stage mediated feedback loop.

Intensity-dependent timing and precision of startle response latency in larval zebrafish.

Key Points: Using high-speed videos time-locked with whole-animal electrical recordings, simultaneous measurement of behavioural kinematics and field potential parameters of C-start startle responses allowed for discrimination between short-latency and long-latency C-starts (SLCs vs. LLCs) in larval zebrafish. Apart from their latencies, SLC kinematics and SLC field potential parameters were intensity independent.

Sequence-dependent nanometer-scale conformational dynamics of individual RecBCD-DNA complexes.

RecBCD is a multifunctional enzyme that possesses both helicase and nuclease activities. To gain insight into the mechanism of its helicase function, RecBCD unwinding at low adenosine triphosphate (ATP) (2-4 μM) was measured using an optical-trapping assay featuring 1 base-pair (bp) precision. Instead of uniformly sized steps, we observed forward motion convolved with rapid, large-scale (∼4 bp) variations in DNA length.

Sensorimotor structure of Drosophila larva phototaxis.

The avoidance of light by fly larvae is a classic paradigm for sensorimotor behavior. Here, we use behavioral assays and video microscopy to quantify the sensorimotor structure of phototaxis using the Drosophila larva. Larval locomotion is composed of sequences of runs (periods of forward movement) that are interrupted by abrupt turns, during which the larva pauses and sweeps its head back and forth, probing local light information to determine the direction of the successive run.

Back-scattered detection yields viable signals in many conditions.

Precision position-sensing is required for many microscopy techniques. One promising method, back-scattered detection (BSD), is incredibly sensitive, allowing for position measurements at the level of tens of picometers in three dimensions. In BSD the position of a micron-sized bead is measured by back-scattering a focused laser beam off the bead and imaging the resulting interference pattern onto a detector.

Ultrastable atomic force microscopy: atomic-scale stability and registration in ambient conditions.

Instrumental drift in atomic force microscopy (AFM) remains a critical, largely unaddressed issue that limits tip-sample stability, registration, and the signal-to-noise ratio during imaging. By scattering a laser off the apex of a commercial AFM tip, we locally measured and thereby actively controlled its three-dimensional position above a sample surface to <40 pm (Deltaf = 0.01-10 Hz) in air at room temperature.

Precision surface-coupled optical-trapping assay with one-basepair resolution.

The most commonly used optical-trapping assays are coupled to surfaces, yet such assays lack atomic-scale ( approximately 0.1 nm) spatial resolution due to drift between the surface and trap. We used active stabilization techniques to minimize surface motion to 0.

Back-scattered detection provides atomic-scale localization precision, stability, and registration in 3D.

State-of-the-art microscopy techniques (e.g., atomic force microscopy, scanning-tunneling microscopy, and optical tweezers) are sensitive to atomic-scale (100 pm) displacements.

Stabilization of an optical microscope to 0.1 nm in three dimensions.

Mechanical drift is a long-standing problem in optical microscopy that occurs in all three dimensions. This drift increasingly limits the resolution of advanced surface-coupled, single-molecule experiments. We overcame this drift and achieved atomic-scale stabilization (0.