27 research outputs found
Human base excision repair complex is physically associated to DNA replication and cell cycle regulatory proteins
It has been hypothesized that a replication associated repair pathway operates on base damage and single strand breaks (SSB) at replication forks. In this study, we present the isolation from the nuclei of human cycling cells of a multiprotein complex containing most of the essential components of base excision repair (BER)/SSBR, including APE1, UNG2, XRCC1 and POLĪ², DNA PK, replicative POLĪ±, Ī“ and É, DNA ligase 1 and cell cycle regulatory protein cyclin A. Co-immunoprecipitation revealed that in this complex DNA repair proteins are physically associated to cyclin A and to DNA replication proteins including MCM7. This complex is endowed with DNA polymerase and protein kinase activity and is able to perform BER of uracil and AP sites. This finding suggests that a preassembled DNA repair machinery is constitutively active in cycling cells and is ready to be recruited at base damage and breaks occurring at replication forks
The type of DNA glycosylase determines the base excision repair pathway in mammalian cells.
The base excision repair (BER) of modified nucleotides is initiated by damage-specific DNA glycosylases. The repair of the resulting apurinic/apyrimidinic site involves the replacement of either a single nucleotide (short patch BER) or of several nucleotides (long patch BER). The mechanism that controls the selection of either BER pathway is unknown. We tested the hypothesis that the type of base damage present on DNA, by determining the specific DNA glycosylase in charge of its excision, drives the repair of the resulting abasic site intermediate to either BER branch. In mammalian cells hypoxanthine (HX) and 1,N6-ethenoadenine (epsilonA) are both substrates for the monofunctional 3-methyladenine DNA glycosylase, the ANPG protein, whereas 7,8-dihydro-8-oxoguanine (8-oxoG) is removed by the bifunctional DNA glycosylase/beta-lyase 8-oxoG-DNA gly- cosylase (OGG1). Circular plasmid molecules containing a single HX, epsilonA, or 8-oxoG were constructed. In vitro repair assays with HeLa cell extracts revealed that HX and epsilonA are repaired via both short and long patch BER, whereas 8-oxoG is repaired mainly via the short patch pathway. The preferential repair of 8-oxoG by short patch BER was confirmed by the low efficiency of repair of this lesion by DNA polymerase beta-deficient mouse cells as compared with their wild-type counterpart. These data fit into a model where the intrinsic properties of the DNA glycosylase that recognizes the lesion selects the branch of BER that will restore the intact DNA template
Are there more galaxies than we see around high- quasars?
Whether or not quasars lie in the most massive dark-matter
halos of the Universe is still a subject of dispute. While most theoretical
studies support this scenario, current observations yield discordant results
when they probe the halo mass through the detection rate of quasar companion
galaxies. Feedback processes from supermassive black holes and dust obscuration
have been blamed for this discrepancy, but the impact of these effects is
complex and far from being clearly understood. This paper aims to improve the
interpretation of current far-infrared observations by taking into account the
cosmological volume probed by the Atacama Large Millimeter/submillimeter Array
Telescope and to explain the observational discrepancies. We statistically
investigate the detection rate of quasar companions in current observations and
verify if they match the expected distribution from various theoretical models,
once convolved with the ALMA field-of-view, through the use of Monte Carlo
simulations. We demonstrate that the telescope geometrical bias is fundamental
and can alone explain the scatter in the number of detected satellite galaxies
in different observations. We conclude that the resulting companion densities
depend on the chosen galaxy distributions. According to our fiducial models,
current data favour a density scenario where quasars lie in dark-matter halos
of viral mass , in agreement with
most theoretical studies. According to our analysis, each quasar has about 2
companion galaxies, with a [CII] luminosity , within a distance of about 1~Mpc from the quasar.Comment: 7 pages, 5 figures; accepted for publications in A&
Nighttime Sugar Starvation Orchestrates Gibberellin Biosynthesis and Plant Growth in Arabidopsis
Misexpression of a chloroplast aspartyl protease leads to severe growth defects and alters carbohydrate metabolism in Arabidopsis
The crucial role of carbohydrate in plant growth and morphogenesis is widely recognized. In this study, we describe the characterization of nana, a dwarf Arabidopsis (Arabidopsis thaliana) mutant impaired in carbohydrate metabolism. We show that the nana dwarf phenotype was accompanied by altered leaf morphology and a delayed flowering time. Our genetic and molecular data indicate that the mutation in nana is due to a transfer DNA insertion in the promoter region of a gene encoding a chloroplast-located aspartyl protease that alters its pattern of expression. Overexpression of the gene (oxNANA) phenocopies the mutation. Both nana and oxNANA display alterations in carbohydrate content, and the extent of these changes varies depending on growth light intensity. In particular, in low light, soluble sugar levels are lower and do not show the daily fluctuations observed in wild-type plants. Moreover, nana and oxNANA are defective in the expression of some genes implicated in sugar metabolism and photosynthetic light harvesting. Interestingly, some chloroplast-encoded genes as well as genes whose products seem to be involved in retrograde signaling appear to be down-regulated. These findings suggest that the NANA aspartic protease has an important regulatory function in chloroplasts that not only influences photosynthetic carbon metabolism but also plastid and nuclear gene expression
Bubbles and outflows: the novel JWST/NIRSpec view of the z=1.59 obscured quasar XID2028
Quasar feedback in the form of powerful outflows is invoked as a key
mechanism to quench star formation in galaxies, although direct observational
evidence is still scarce and debated. Here we present Early Release Science
JWST NIRSpec IFU observations of the z=1.59 prototypical obscured quasar
XID2028: this target represents a unique test case to study QSO feedback at the
peak epoch of AGN-galaxy co-evolution thanks to its existing extensive
multi-wavelength coverage and massive and extended outflow detected both in the
ionised and molecular components. With the unprecedented sensitivity and
spatial resolution of JWST, the NIRSpec dataset reveals a wealth of structures
in the ionised gas kinematics and morphology previously hidden in the
seeing-limited ground-based data. In particular, we find evidence of
interaction between the interstellar medium of the galaxy and the QSO-driven
outflow and radio jet, which is producing an expanding bubble from which the
fast and extended wind detected in previous observations is emerging. The new
observations confirm the complex interplay between the AGN jet/wind and the ISM
of the host galaxy, highlighting the role of low luminosity radio jets in AGN
feedback, and showcase the new window opened by NIRSpec on the detailed study
of feedback at high redshift.Comment: 12 pages, 11 figures, submitted to A&A. Comments welcom
A fast-rotator post-starburst galaxy quenched by supermassive black-hole feedback at z=3
There is compelling evidence that the most massive galaxies in the Universe
stopped forming stars due to the time-integrated feedback from their central
super-massive black holes (SMBHs). However, the exact quenching mechanism is
not yet understood, because local massive galaxies were quenched billions of
years ago. We present JWST/NIRSpec integral-field spectroscopy observations of
GS-10578, a massive, quiescent galaxy at redshift z=3.064. From the spectrum we
infer that the galaxy has a stellar mass of MSun
and a dynamical mass MSun. Half of its
stellar mass formed at z=3.7-4.6, and the system is now quiescent, with the
current star-formation rate SFR<9 MSun/yr. We detect ionised- and neutral-gas
outflows traced by [OIII] emission and NaI absorption. Outflow velocities reach
1,000 km/s, comparable to the galaxy escape velocity and
too high to be explained by star formation alone. GS-10578 hosts an Active
Galactic Nucleus (AGN), evidence that these outflows are due to SMBH feedback.
The outflow rates are 0.14-2.9 and 30-300 MSun/yr for the ionised and neutral
phases, respectively. The neutral outflow rate is ten times higher than the
SFR, hence this is direct evidence for ejective SMBH feedback, with
mass-loading capable of interrupting star formation by rapidly removing its
fuel. Stellar kinematics show ordered rotation, with spin parameter
, meaning GS-10578 is rotation supported. This study
shows direct evidence for ejective AGN feedback in a massive, recently quenched
galaxy, thus clarifying how SMBHs quench their hosts. Quenching can occur
without destroying the stellar disc.Comment: 40 pages, 9 figures, submitted to Nat. Ast., comments welcome
JADES: Probing interstellar medium conditions at with ultra-deep JWST/NIRSpec spectroscopy
We present emission line ratios from a sample of 26 Lyman break galaxies from
with , measured from ultra-deep
JWST/NIRSpec MSA spectroscopy from JADES. We use 28 hour deep PRISM/CLEAR and 7
hour deep G395M/F290LP observations to measure, or place strong constraints on,
ratios of widely studied rest-frame optical emission lines including H,
H, [OII] 3726,3729, [NeIII] 3869, [OIII]
4959, [OIII] 5007, [OI] 6300, [NII] 6583,
and [SII] 6716,6731 in individual spectra. We find that
the emission line ratios exhibited by these galaxies occupy
clearly distinct regions of line-ratio space compared to typical z~0-3
galaxies, instead being more consistent with extreme populations of
lower-redshift galaxies. This is best illustrated by the [OIII]/[OII] ratio,
tracing interstellar medium (ISM) ionisation, in which we observe more than
half of our sample to have [OIII]/[OII]>10. Our high signal-to-noise spectra
reveal more than an order of magnitude of scatter in line ratios such as
[OII]/H and [OIII]/[OII], indicating significant diversity in the ISM
conditions within the sample. We find no convincing detections of [NII] in our
sample, either in individual galaxies, or a stack of all G395M/F290LP spectra.
The emission line ratios observed in our sample are generally consistent with
galaxies with extremely high ionisation parameters (log ), and a
range of metallicities spanning from to higher than
, suggesting we are probing low-metallicity systems
undergoing periods of rapid star-formation, driving strong radiation fields.
These results highlight the value of deep observations in constraining the
properties of individual galaxies, and hence probing diversity within galaxy
population.Comment: 20 pages, 9 figures, submitted to Astronomy & Astrophysics, updated
values in table
The JADES Origins Field: A New JWST Deep Field in the JADES Second NIRCam Data Release
We summarize the properties and initial data release of the JADES Origins
Field (JOF), which will soon be the deepest imaging field yet observed with the
James Webb Space Telescope (JWST). This field falls within the GOODS-S region
about 8' south-west of the Hubble Ultra Deep Field (HUDF), where it was formed
initially in Cycle 1 as a parallel field of HUDF spectroscopic observations
within the JWST Advanced Deep Extragalactic Survey (JADES). This imaging will
be greatly extended in Cycle 2 program 3215, which will observe the JOF for 5
days in six medium-band filters, seeking robust candidates for z>15 galaxies.
This program will also include ultra-deep parallel NIRSpec spectroscopy (up to
104 hours on-source, summing over the dispersion modes) on the HUDF. Cycle 3
observations from program 4540 will add 20 hours of NIRCam slitless
spectroscopy to the JOF. With these three campaigns, the JOF will be observed
for 380 open-shutter hours with NIRCam using 15 imaging filters and 2 grism
bandpasses. Further, parts of the JOF have deep 43 hr MIRI observations in
F770W. Taken together, the JOF will soon be one of the most compelling deep
fields available with JWST and a powerful window into the early Universe. This
paper presents the second data release from JADES, featuring the imaging and
catalogs from the year 1 JOF observations.Comment: Submitted to ApJ Supplement. Images and catalogs are available at
https://archive.stsci.edu/hlsp/jades . A FITSmap portal to view the images is
at https://jades.idies.jhu.ed
JADES NIRSpec Spectroscopy of GN-z11: Lyman- emission and possible enhanced nitrogen abundance in a luminous galaxy
We present JADES JWST/NIRSpec spectroscopy of GN-z11, the most luminous
candidate Lyman break galaxy in the GOODS-North field with
. We derive a redshift of (lower than previous
determinations) based on multiple emission lines in our low and medium
resolution spectra over m. We significantly detect the continuum
and measure a blue rest-UV spectral slope of . Remarkably, we see
spatially-extended Lyman- in emission (despite the highly-neutral IGM
expected at this early epoch), offset 555 km/s redward of the systemic
redshift. From our measurements of collisionally-excited lines of both low- and
high-ionization (including [O II] , [Ne III] and C
III] ) we infer a high ionization parameter (). We
detect the rarely-seen N IV] and N III] lines in
both our low and medium resolution spectra, with other high ionization lines
seen in low resolution spectrum such as He II (blended with O III]) and C IV
(with a possible P-Cygni profile). Based on the observed rest-UV line ratios,
we cannot conclusively rule out photoionization from AGN. The high C III]/He II
ratios, however, suggest a likely star-formation explanation. If the observed
emission lines are powered by star formation, then the strong N III]
observed may imply an unusually high abundance. Balmer
emission lines (H, H) are also detected, and if powered by star
formation rather than an AGN we infer a star formation rate of (depending on the IMF) and low dust attenuation. Our
NIRSpec spectroscopy confirms that GN-z11 is a remarkable galaxy with extreme
properties seen 430 Myr after the Big Bang.Comment: Submitted to Astronomy & Astrophysics, 14 pages, 9 figure