Human origin recognition complex is essential for HP1 binding to chromatin and heterochromatin organization

The origin recognition complex (ORC) is a DNA replication initiator protein also known to be involved in diverse cellular functions including gene silencing, sister chromatid cohesion, telomere biology, heterochromatin localization, centromere and centrosome activity, and cytokinesis. We show that, in human cells, multiple ORC subunits associate with hetereochromatin protein 1 (HP1) alpha- and HP1beta-containing heterochromatic foci. Fluorescent bleaching studies indicate that multiple subcomplexes of ORC exist at heterochromatin, with Orc1 stably associating with heterochromatin in G1 phase, whereas other ORC subunits have transient interactions throughout the cell-division cycle. Both Orc1 and Orc3 directly bind to HP1alpha, and two domains of Orc3, a coiled-coil domain and a mod-interacting region domain, can independently bind to HP1alpha; however, both are essential for in vivo localization of Orc3 to heterochromatic foci. Direct binding of both Orc1 and Orc3 to HP1 suggests that, after the degradation of Orc1 at the G1/S boundary, Orc3 facilitates assembly of ORC/HP1 proteins to chromatin. Although depletion of Orc2 and Orc3 subunits by siRNA caused loss of HP1alpha association to heterochromatin, loss of Orc1 and Orc5 caused aberrant HP1alpha distribution only to pericentric heterochromatin-surrounding nucleoli. Depletion of HP1alpha from human cells also shows loss of Orc2 binding to heterochromatin, suggesting that ORC and HP1 proteins are mutually required for each other to bind to heterochromatin. Similar to HP1alpha-depleted cells, Orc2 and Orc3 siRNA-treated cells also show loss of compaction at satellite repeats, suggesting that ORC together with HP1 proteins may be involved in organizing higher-order chromatin structure and centromere function

Universal power law in the orientational relaxation in thermotropic liquid crystals

We observe a surprisingly general power law decay at short to intermediate times in orientational relaxation in a variety of model systems (both calamitic and discotic, and also discrete) for thermotropic liquid crystals. As all these systems transit across the isotropic-nematic phase boundary, two power law relaxation regimes, separated by a plateau, emerge giving rise to a step-like feature (well-known in glassy liquids) in the single-particle second-rank orientational time correlation function. In contrast to its probable dynamical origin in supercooled liquids, we show that the power law here can originate from the thermodynamic fluctuations of the orientational order parameter, driven by the rapid growth in the second-rank orientational correlation length.Comment: Submitted to Physical Review Letter

Complete breakdown of the Debye model of rotational relaxation near the isotropic-nematic phase boundary: Effects of intermolecular correlations in orientational dynamics

The Debye-Stokes-Einstein (DSE) model of rotational diffusion predicts that the rotational correlation times $\tau_{l}$ vary as $[l(l+1)]^{-1}$, where $l$ is the rank of the orientational correlation function (given in terms of the Legendre polynomial of rank $l$). One often finds significant deviation from this prediction, in either direction. In supercooled molecular liquids where the ratio $\tau_{1}/\tau_{2}$ falls considerably below three (the Debye limit), one usually invokes a jump diffusion model to explain the approach of the ratio $\tau_{1}/\tau_{2}$ to unity. Here we show in a computer simulation study of a standard model system for thermotropic liquid crystals that this ratio becomes much less than unity as the isotropic-nematic phase boundary is approached from the isotropic side. Simultaneously, the ratio $\tau_2/\eta$ (where $\eta$ is the shear viscosity of the liquid) becomes {\it much larger} than hydrodynamic value near the I-N transition. We have also analyzed the break down of the Debye model of rotational diffusion in ratios of higher order rotational correlation times. We show that the break down of the DSE model is due to the growth of orientational pair correlation and provide a mode coupling theory analysis to explain the results.Comment: Submitted to Physical Review

Dynamic Gaits and Control in Flexible Body Quadruped Robot

Legged robots are highly attractive for military purposes such as carrying heavy loads on uneven terrain for long durations because of the higher mobility they give on rough terrain compared to wheeled vehicles/robots. Existing state-of-the-art quadruped robots developed by Boston Dynamics such as LittleDog and BigDog do not have flexible bodies. It can be easily seen that the agility of quadruped animals such as dogs, cats, and deer etc. depend to a large extent on their ability to flex their bodies. However, simulation study on step climbing in 3D terrain quadruped robot locomotion with flexible body has not been reported in literature. This paper aims to study the effect of body flexibility on stability and energy efficiency in walking mode, trot mode and running (bounding) mode on step climbing

Current distribution of the invasive earthworm Pontoscolex corethrurus (Müller, 1857) after a century of its first report from Kerala state, India

Pontoscolex corethrurus (Müller, 1857) is an important peregrine earthworm species in the humid tropics and is found in land disturbed by human activities. Its presence in Kerala state was first reported by Michaelsen in 1910. So far the occurrence of 14 exotic earthworm species has been reported from Kerala state. However present distribution status of any of these exotic species is not yet thoroughly studied. Now P. corethrurus is naturalized in forests, degraded areas, and agroecosystems from the higher altitude areas to the coastal zones. Here, the current distribution pattern of P. corethrurus in the state after a period of 100 years is highlighted

Lidar observations of sporadic Na layers over Gadanki (13.5° N, 79.2° E)

International audienceWe studied the characteristics of sporadic sodium layers (SSLs) observed with the sodium (Na) resonance scattering lidar at Gadanki (13.5° N, 79.2° E). The SSLs were observed on a total of 63 occasions during 464 h of Na lidar observations from January 2005 to February 2006. The observations showed that one SSL event occurred, on average, every 7 h. The most prominent sporadic layer, which formed on 12 February 2005, exhibited a peak density of 60 722 Na atoms/cm³ around 92 km and it was nearly twice the peak density reported from elsewhere using ground-based observations. In general, the SSLs exhibited the following characteristics: (1) they developed at heights between 88 and 98 km with an average height around 94 km; (2) maximum density occurred during the early morning hours between 02:00 and 05:00 IST; (3) the ratio of the maximum peak Na density to the average density was normally around 3 to 5 and it exceeded even 10 in some cases; (4) the events lasted from a few minutes to several hours. The formation period of the SSLs was longer compared to the decay period of the SSLs. Most of the SSL events showed downward motions

SRSF1 modulates the organization of splicing factors in nuclear speckles and regulates transcription

The mammalian cell nucleus is compartmentalized into non-membranous subnuclear domains that regulate key nuclear functions. Nuclear speckles are subnuclear domains that contain pre-mRNA processing factors and non-coding RNAs. Many of the nuclear speckle constituents work in concert to coordinate multiple steps of gene expression, including transcription, pre-mRNA processing and mRNA transport. The mechanism that regulates the formation and maintenance of nuclear speckles in the interphase nucleus is poorly understood. In the present study, we provide evidence for the involvement of nuclear speckle resident proteins and RNA components in the organization of nuclear speckles. SR-family splicing factors and their binding partner, long non-coding MALAT1 RNA, can nucleate the assembly of nuclear speckles in the interphase nucleus. Depletion of SRSF1 in human cells compromises the association of splicing factors to nuclear speckles and influences the levels and activity of other SR proteins. Furthermore, on a stably integrated reporter gene locus, we demonstrate the role for SRSF1 in RNA polymerase II-mediated transcription. Our results suggest that SR proteins mediate the assembly of nuclear speckles and regulate gene expression by influencing both transcriptional and posttranscriptional activities within the cell nucleus