Regulation of chromatin structure involves histone posttranslational modifications that can modulate intrinsic properties of the chromatin fiber to change the chromatin state. We used chemically defined nucleosome arrays to demonstrate that H2B ubiquitylation (uH2B), a modification associated with transcription, interferes with chromatin compaction and leads to an open and biochemically accessible fiber conformation. Notably, these effects were specific for ubiquitin, as compaction of chromatin modified with a similar ubiquitin-sized protein, Hub1, was only weakly affected. Applying a fluorescence-based method, we found that uH2B acts through a mechanism distinct from H4 tail acetylation, a modification known to disrupt chromatin folding. Finally, incorporation of both uH2B and acetylated H4 resulted in synergistic inhibition of higher-order chromatin structure formation, possibly a result of their distinct modes of action.

Histone H2B ubiquitylation disrupts local and higher-order chromatin compaction

Excitation energy transfer, trapping and annihilation in photosynthetic systems

We report recent achievements in metal-enhanced fluorescence from our laboratory Several fluorophore systems have been studied on metal particle-coated surfaces and in colloid suspensions In particular, we describe a distance dependent enhancement on silver island films (SIFs), release of self-quenching of fluorescence near silver particles, and the applications of fluorescence enhancement near metalized surfaces to bioassays We discuss a number of methods for various shaped silver particle deposition on surfaces

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Advances in surface-enhanced fluorescence.

We report the synthesis, characterization, and covalent surface chemistry of “magnetomicelles”, cross-linked, amphiphilic block-copolymer micelles that encapsulate superparamagnetic iron oxide nanoparticles. Because these composite nanostructures assemble spontaneously from solution by simultaneous desolvation of nanoparticle and amphiphilic poly(styrene250-block-acrylic acid13) components, explicit surface functionalization of the particles is not required, and the encapsulation method was applied to different magnetic nanoparticle sizes and compositions. TEM images of the magnetomicelles illustrated that the number of encapsulated particles could be dictated rationally by synthetic conditions. The magnetic properties of the particles were characterized by SQUID magnetometry and followed the general Langevin magnetic model for superparamagnetic materials. The micellar shells of these particles were functionalized using covalent chemistry that would not ordinarily be possible on the magnetic particle surf...

Magnetomicelles: Composite Nanostructures from Magnetic Nanoparticles and Cross-Linked Amphiphilic Block Copolymers

Release of the self-quenching of fluorescence near silver metallic surfaces

The problem of radiationless electronic excitation energy transfer in isotropic media has lost none of its interest although it has been under investigation for more than 50 years. On the grounds of classical physics, Perrin (1925) had already predicted that the electromagnetic field of an excited oscillator would induce forced oscillations of an unexcited oscillator at the same frequencies, considering the interacting molecules as linear oscillators, thus resulting in energy transfer from an excited to an unexcited molecule. Such a process of energy transfer occurs when the separation between the interacting oscillators is not large (up to about 10 nm), when their oscillations are approximately equivalent. The theory of Perrin (1925). as well as its quantummechanical modification (Perrin, 1932), did not yield results consistent with experimental data. The quantum-mechanical theory of very weak interactions in isotropic media was later developed by Forster (1946, 1948a), Galanin (1955) and Dexter (1953), who demonstrated that the rate of energy transfer could be related to the probability of the emission and absorption transitions in the interacting molecules. According to Forster (1948a), the rate of radiationless excitation energy transfer, pDA, is given by

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1751-1097.1983.tb03372.x

Excitation energy transfer and its manifestation in isotropic media

— Dichroism was measured for different electronic transitions (SnSo) of Y-4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazo-1,2-a purine (Yt base) in anisotropic polyvinylalcohol (PVA) films. The directions of the electronic transition moments of the Yt base were determined based on the results obtained, applying the models of Tanizaki and Popov. The results were compared with relevant data obtained from quantum chemical calculations.

A. Kawski

Papers

Excitation energy transfer and its manifestation in isotropic media

DIRECTIONS OF THE ELECTRONIC TRANSITION MOMENTS OF SYNTHETIC Yt BASE