Structural insights into distinct mechanisms of RNA polymerase II and III recruitment to snRNA promoters.

RNA polymerase III (Pol III) transcribes short, essential RNAs, including the U6 small nuclear RNA (snRNA). At U6 snRNA genes, Pol III is recruited by the snRNA Activating Protein Complex (SNAPc) and a Brf2-containing TFIIIB complex, forming a pre-initiation complex (PIC). Uniquely, SNAPc also recruits Pol II at the remaining splicesosomal snRNA genes (U1, 2, 4 and 5).

Structural basis of SNAPc-dependent snRNA transcription initiation by RNA polymerase II.

RNA polymerase II (Pol II) carries out transcription of both protein-coding and non-coding genes. Whereas Pol II initiation at protein-coding genes has been studied in detail, Pol II initiation at non-coding genes, such as small nuclear RNA (snRNA) genes, is less well understood at the structural level. Here, we study Pol II initiation at snRNA gene promoters and show that the snRNA-activating protein complex (SNAPc) enables DNA opening and transcription initiation independent of TFIIE and TFIIH in vitro.

Human Condensin I and II Drive Extensive ATP-Dependent Compaction of Nucleosome-Bound DNA.

Structural maintenance of chromosomes (SMC) complexes are essential for genome organization from bacteria to humans, but their mechanisms of action remain poorly understood. Here, we characterize human SMC complexes condensin I and II and unveil the architecture of the human condensin II complex, revealing two putative DNA-entrapment sites. Using single-molecule imaging, we demonstrate that both condensin I and II exhibit ATP-dependent motor activity and promote extensive and reversible compaction of double-stranded DNA.

Phase behavior of poly(N-isopropylacrylamide) nanogel dispersions: temperature dependent particle size and interactions.

The phase behavior of poly(N-isopropylacrylamide) nanoparticles dispersed in aqueous medium is investigated as a function of temperature using static and dynamic light scattering techniques. The diameter, d of the particles, as determined by dynamic light scattering measurements on dilute dispersion showed a decrease in size from 273 nm at 25 degrees C to 114 nm at 40 degrees C as function of temperature with a sudden collapse of particle volume (volume phase transition) at 32.4 degrees C.

Random hcp and fcc structures in thermoresponsive microgel crystals.

Monodisperse thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles having a diameter of 520 nm were synthesized by free-radical precipitation polymerization and centrifuged to obtain a concentrated suspension. The centrifuged mother suspension was made to self-order into a crystalline state by repeated annealing beyond the volume phase transition (VPT) of the particles. We report here the three-dimensional (3D) real space structure, determined using a confocal laser scanning microscope, of PNIPAM microgel crystal samples prepared by two different recrystallized routes: (1) solidifying a shear melted colloidal liquid (referred as as-prepared sample) and (2) slow cooling of a colloidal liquid (referred as recrystallized sample).