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Abstract Background The carboxy termini of proteins are a frequent site of activity for a variety of biologically important functions, ranging from post-translational modification to protein targeting. Several short peptide motifs involved in protein sorting roles and dependent upon their proximity to the C-terminus for proper function have already been characterized. As a limited number of such motifs have been identified, the potential exists for genome-wide statistical analysis and comparative genomics to reveal novel peptide signatures functioning in a C-terminal dependent manner. We have applied a novel methodology to the prediction of C-terminal-anchored peptide motifs involving a simple z-statistic and several techniques for improving the signal-to-noise ratio. Results We examined the statistical over-representation of position-specific C-terminal tripeptides in 7 eukaryotic proteomes. Sequence randomization models and simple-sequence masking were applied to the successful reduction of background noise. Similarly, as C-terminal homology among members of large protein families may artificially inflate tripeptide counts in an irrelevant and obfuscating manner, gene-family clustering was performed prior to the analysis in order to assess tripeptide over-representation across protein families as opposed to across all proteins. Finally, comparative genomics was used to identify tripeptides significantly occurring in multiple species. This approach has been able to predict, to our knowledge, all C-terminally anchored targeting motifs present in the literature. These include the PTS1 peroxisomal targeting signal (SKL*), the ER-retention signal (K/HDEL*), the ER-retrieval signal for membrane bound proteins (KKxx*), the prenylation signal (CC*) and the CaaX box prenylation motif. In addition to a high statistical over-representation of these known motifs, a collection of significant tripeptides with a high propensity for biological function exists between species, among kingdoms and across eukaryotes. Motifs of note include a serine-acidic peptide (DSD*) as well as several lysine enriched motifs found in nearly all eukaryotic genomes examined. Conclusion We have successfully generated a high confidence representation of eukaryotic motifs anchored at the C-terminus. A high incidence of true-positives in our results suggests that several previously unidentified tripeptide patterns are strong candidates for representing novel peptide motifs of a widely employed nature in the C-terminal biology of eukaryotes. Our application of comparative genomics, statistical over-representation and the adjustment for protein family homology has generated several hypotheses concerning the C-terminal topology as it pertains to sorting and potential protein interaction signals. This approach to background reduction could be expanded for application to protein motif prediction in the protein interior. A parallel N-terminal analysis is presented as supplementary data.

Abstract Background A great deal is known about the morphological endpoints of plant cell death, but relatively little is known about its sequence of events and / or its execution at the biochemical level. Live cell imaging using GFP-tagged markers is a powerful way to provide dynamic portraits of a cellular process that can in turn provide a descriptive foundation valuable for future biochemical and genetic investigations. Results While characterizing a collection of random GFP-protein fusion markers we discovered that mechanical wounding induces rapid aggregation of a GFP-Nitrilase 1 fusion protein in Arabidopsis cells directly abutting wound sites. Time-lapse imaging of this response shows that the aggregation occurs in cells that subsequently die 30 – 60 minutes post-wounding, indicating that GFP-Nit1 aggregation is an early marker of cell death at wound sites. Time-lapse confocal imaging was used to characterize wound-induced cell death using GFP-Nit1 and markers of the nucleus and endoplasmic reticulum. These analyses provide dynamic portraits of well-known death-associated responses such as nuclear contraction and cellular collapse and reveal novel features such as nuclear envelope separation, ER vesiculation and loss of nuclear-lumen contents. As a parallel system for imaging cell death, we developed a chemical method for rapidly triggering cell death using the herbicides bromoxynil or chloroxynil which cause rapid GFP-Nit1 aggregation, loss of nuclear contents and cellular collapse, but not nuclear contraction, separating this response from others during plant cell death. Conclusion Our observations place aggregation of Nitrilase 1 as one of the earliest events associated with wound and herbicide-induced cell death and highlight several novel cellular events that occur as plant cells die. Our data create a detailed descriptive framework for future investigations of plant cell death and provide new tools for both its cellular and biochemical analysis.

Early JWST observations have uncovered a population of red sources that might represent a previously overlooked phase of supermassive black hole growth 1-3 . One of the most intriguing examples is an extremely red, point-like object that was found to be triply imaged by the strong lensing cluster Abell 2744 (ref.  4 ). Here we present deep JWST/NIRSpec observations of this object, Abell2744-QSO1. The spectroscopy confirms that the three images are of the same object, and that it is a highly reddened (A V  ≃ 3) broad emission line active galactic nucleus at a redshift of z spec  = 7.0451 ± 0.0005. From the width of Hβ (full width at half-maximum = 2,800 ± 250 km s -1 ), we derive a black hole mass of M BH = 4 - 1 + 2 × 1 0 7 M ⊙ . We infer a very high ratio of black-hole-to-galaxy mass of at least 3%, an order of magnitude more than that seen in local galaxies 5 and possibly as high as 100%. The lack of strong metal lines in the spectrum together with the high bolometric luminosity (L bol  = (1.1 ± 0.3) × 10 45  erg s -1 ) indicate that we are seeing the black hole in a phase of rapid growth, accreting at 30% of the Eddington limit. The rapid growth and high black-hole-to-galaxy mass ratio of Abell2744-QSO1 suggest that it may represent the missing link between black hole seeds 6 and one of the first luminous quasars 7 ., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

The identification of sources driving cosmic reionization, a major phase transition from neutral hydrogen to ionized plasma around 600-800 Myr after the Big Bang 1-3 , has been a matter of debate 4 . Some models suggest that high ionizing emissivity and escape fractions (f esc ) from quasars support their role in driving cosmic reionization 5,6 . Others propose that the high f esc values from bright galaxies generate sufficient ionizing radiation to drive this process 7 . Finally, a few studies suggest that the number density of faint galaxies, when combined with a stellar-mass-dependent model of ionizing efficiency and f esc , can effectively dominate cosmic reionization 8,9 . However, so far, comprehensive spectroscopic studies of low-mass galaxies have not been done because of their extreme faintness. Here we report an analysis of eight ultra-faint galaxies (in a very small field) during the epoch of reionization with absolute magnitudes between M UV  ≈ -17 mag and -15 mag (down to 0.005L ⋆ (refs.  10,11 )). We find that faint galaxies during the first thousand million years of the Universe produce ionizing photons with log[ξ ion  (Hz erg -1 )] = 25.80 ± 0.14, a factor of 4 higher than commonly assumed values 12 . If this field is representative of the large-scale distribution of faint galaxies, the rate of ionizing photons exceeds that needed for reionization, even for escape fractions of the order of 5%., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Research shows that people characterized as repressors display inhibited recall for unpleasant memories. In this study, the relationship between repressive coping style and the recall of affect near the time of the experience was compared to delayed recall. An experience sampling technique was used to collect affect data twice daily for 4 weeks. Repressive coping style was found to be related to low levels of average daily unpleasant affect and lowered delayed recall of unpleasant affect. Unlike repressors, high anxious individuals overestimated unpleasant affect during delayed recall. Repressors did not exhibit isolation of the dominant unpleasant affect from nondominant unpleasant affect in daily reporting. The overall pattern of results suggests that the effect of repressive coping style is to diminish the encoding of all unpleasant affect, whereas trait anxiety appears to promote overestimation in the recall of unpleasant affect.

Although individuals differ widely in the typical intensity of their affective experience, the mechanisms that create or maintain these differences are unclear. Larsen, Diener, and Cropanzano (1987) examined the hypothesis that individual differences in affect intensity (AI) are related to how people interpret emotional stimuli. They found that high AI individuals engaged in more personalizing and generalizing cognitions while construing emotional stimuli than low AI individuals. The present study extends these findings by examining cognitive activity during a different task-the generation of information to communicate about life events. Participants provided free-response descriptions of 16 life events. These descriptions were content coded for five informational style variables. It was found that the descriptive information generated by high AI participants contained significantly more references to emotional arousal, more focus on feelings, and more generalization compared to participants low in AI. These results are consistent with the notion that specific cognitive activity may lead to, or at least be associated with, dispositional affect intensity. In addition, the informational style variables identified in this study were stable over time and consistent across situations. Although men and women differ in AI, this difference becomes insignificant after controlling for informational style variation. Overall results are discussed in terms of a model of various psychological mechanisms that may potentially create or maintain individual differences in affect intensity.