9,001 research outputs found
Imaging and energetics of single SSB-ssDNA molecules reveal intramolecular condensation and insight into RecOR function.
Escherichia coli single-stranded DNA (ssDNA) binding protein (SSB) is the defining bacterial member of ssDNA binding proteins essential for DNA maintenance. SSB binds ssDNA with a variable footprint of âŒ30-70 nucleotides, reflecting partial or full wrapping of ssDNA around a tetramer of SSB. We directly imaged single molecules of SSB-coated ssDNA using total internal reflection fluorescence (TIRF) microscopy and observed intramolecular condensation of nucleoprotein complexes exceeding expectations based on simple wrapping transitions. We further examined this unexpected property by single-molecule force spectroscopy using magnetic tweezers. In conditions favoring complete wrapping, SSB engages in long-range reversible intramolecular interactions resulting in condensation of the SSB-ssDNA complex. RecO and RecOR, which interact with SSB, further condensed the complex. Our data support the idea that RecOR--and possibly other SSB-interacting proteins-function(s) in part to alter long-range, macroscopic interactions between or throughout nucleoprotein complexes by microscopically altering wrapping and bridging distant sites
Envelope Expansion with Core Collapse. III. Similarity Isothermal Shocks in a Magnetofluid
We explore MHD solutions for envelope expansions with core collapse (EECC)
with isothermal MHD shocks in a quasi-spherical symmetry and outline potential
astrophysical applications of such magnetized shock flows. MHD shock solutions
are classified into three classes according to the downstream characteristics
near the core. Class I solutions are those characterized by free-fall collapses
towards the core downstream of an MHD shock, while Class II solutions are those
characterized by Larson-Penston (LP) type near the core downstream of an MHD
shock. Class III solutions are novel, sharing both features of Class I and II
solutions with the presence of a sufficiently strong magnetic field as a
prerequisite. Various MHD processes may occur within the regime of these
isothermal MHD shock similarity solutions, such as sub-magnetosonic
oscillations, free-fall core collapses, radial contractions and expansions. We
can also construct families of twin MHD shock solutions as well as an
`isothermal MHD shock' separating two magnetofluid regions of two different yet
constant temperatures. The versatile behaviours of such MHD shock solutions may
be utilized to model a wide range of astrophysical problems, including star
formation in magnetized molecular clouds, MHD link between the asymptotic giant
branch phase to the proto-planetary nebula phase with a hot central magnetized
white dwarf, relativistic MHD pulsar winds in supernova remnants, radio
afterglows of soft gamma-ray repeaters and so forth.Comment: 21 pages, 33 figures, accepted by MNRA
Recommended from our members
Continuous light-emitting Diode (LED) lighting for improving food quality
Lighting-emitting diodes (LEDs) have shown great potential for plant growth and development, with higher luminous efficiency and positive impact compared with other artificial lighting. The combined effects of red/blue or/and green, and white LED light on plant growth and physiology, including chlorophyll fluorescence, nitrate content and phytochemical concentration before harvest, were investigated. The results showed that continuous light (CL)
exposure at pre-harvest can effectively reduce nitrate
accumulation and increase phytochemical concentrations in lettuce plants, and the former is dependent on the spectral composition and continuous light duration. Lettuce plants grown under continuous combined red and blue (with or without green) LED light with a photosynthetic photon flux density (PPFD) at 200 Ό mol m-2-s-1 exhibited a remarkable decrease of nitrate contents at 24 h compared to other light treatments. In addition, red and blue light (R:B=4:1) was more effective in facilitating lettuce growth than white
LED light at the same PPFD. Moreover, continuous LED light
for 24 h significantly enhanced the free-radical scavenging activity and increased phenolic compound concentrations. In this study, we suggest that a period of continuous LED (R/B)
with green (G) light exposure is needed in order to decrease nitrate concentrations and enhance lettuce quality. 24 h
appears to be the best, but this period should not exceed 48 h. It appears that continuous light could enhance the activity of nitrate reductase leading to a low level of
nitrate content in the leaf. However, the reduction of nitrate is considered to be associated with the circadian clock and the light-signaling pathway as well
- âŠ