Interaction of eukaryotic translation initiation factor 4G with the nuclear cap-binding complex provides a link between nuclear and cytoplasmic functions of the m7 guanosine cap

In eukaryotes the majority of mRNAs have an m7G cap that is added cotranscriptionally and that plays an important role in many aspects of mRNA metabolism. The nuclear cap-binding complex (CBC; consisting of CBP20 and CBP80) mediates the stimulatory functions of the cap in pre-mRNA splicing, 3' end formation, and U snRNA export. As little is known about how nuclear CBC mediates the effects of the cap in higher eukaryotes, we have characterized proteins that interact with CBC in HeLa cell nuclear extracts as potential mediators of its function. Using cross-linking and coimmunoprecipitation, we show that eukaryotic translation initiation factor 4G (eIF4G), in addition to its function in the cytoplasm, is a nuclear CBC-interacting protein. We demonstrate that eIF4G interacts with CBC in vitro and that, in addition to its cytoplasmic localization, there is a significant nuclear pool of eIF4G in mammalian cells in vivo. Immunoprecipitation experiments suggest that, in contrast to the cytoplasmic pool, much of the nuclear eIF4G is not associated with eIF4E (translation cap binding protein of eIF4F) but is associated with CBC. While eIF4G stably associates with spliceosomes in vitro and shows close association with spliceosomal snRNPs and splicing factors in vivo, depletion studies show that it does not participate directly in the splicing reaction. Taken together the data indicate that nuclear eIF4G may be recruited to pre-mRNAs via its interaction with CBC and accompanies the mRNA to the cytoplasm, facilitating the switching of CBC for eIF4F. This may provide a mechanism to couple nuclear and cytoplasmic functions of the mRNA cap structure

Health-related quality of life of Canadian children and youth prenatally exposed to alcohol

BACKGROUND: In Canada, the incidence of Fetal Alcohol Spectrum Disorder (FASD) has been estimated to be 1 in 100 live births. Caused by prenatal exposure to alcohol, FASD is the leading cause of neuro-developmental disabilities among Canadian children, and youth. Objective: To measure the health-related quality of life (HRQL) of Canadian children and youth diagnosed with FASD. METHODS: A prospective cross-sectional study design was used. One-hundred and twenty-six (126) children and youth diagnosed with FASD, aged 8 to 21 years, living in urban and rural communities throughout Canada participated in the study. Participants completed the Health Utilities Index Mark 3 (HUI3). HUI3 measures eight health attributes: vision, hearing, speech, ambulation, dexterity, emotion, cognition, and pain. Utilities were used to measure a single cardinal value between 0 and 1.0 (0 = all-worst health state; 1 = perfect health) to reflect the global HRQL for that child. Mean HRQL scores and range of scores of children and youth with FASD were calculated. A one-sample t-test was used to compare mean HRQL scores of children and youth with FASD to those from the Canadian population. RESULTS: Mean HRQL score of children and youth with FASD was 0.47 (95% CI: 0.42 to 0.52) as compared to a mean score of 0.93 (95% CI: 0.92 to 0.94) in those from the general Canadian population (p < 0.001). Children demonstrated moderate to severe dysfunction on the single-attributes of cognition and emotion. CONCLUSION: Children and youth with FASD have significantly lower HRQL than children and youth from the general Canadian population. This finding has significant implications for practice, policy development, and research

Nucleocytoplasmic transport: a thermodynamic mechanism

The nuclear pore supports molecular communication between cytoplasm and nucleus in eukaryotic cells. Selective transport of proteins is mediated by soluble receptors, whose regulation by the small GTPase Ran leads to cargo accumulation in, or depletion from the nucleus, i.e., nuclear import or nuclear export. We consider the operation of this transport system by a combined analytical and experimental approach. Provocative predictions of a simple model were tested using cell-free nuclei reconstituted in Xenopus egg extract, a system well suited to quantitative studies. We found that accumulation capacity is limited, so that introduction of one import cargo leads to egress of another. Clearly, the pore per se does not determine transport directionality. Moreover, different cargo reach a similar ratio of nuclear to cytoplasmic concentration in steady-state. The model shows that this ratio should in fact be independent of the receptor-cargo affinity, though kinetics may be strongly influenced. Numerical conservation of the system components highlights a conflict between the observations and the popular concept of transport cycles. We suggest that chemical partitioning provides a framework to understand the capacity to generate concentration gradients by equilibration of the receptor-cargo intermediary.Comment: in press at HFSP Journal, vol 3 16 text pages, 1 table, 4 figures, plus Supplementary Material include

Using the cre-lox recombination system to assess functional impairment caused by amino acid substitutions in yeast proteins

A method was developed to assess the functional significance of a sequence motif in yeast Upf3p, a protein required for nonsense-mediated mRNA decay (NMD). The motif lies at the edge of the Upf3p-Upf2p interaction domain, but at the same time resembles the canonical leucine-rich nuclear export sequence (NES) found in proteins that bind Crm1p exportin. To test the function of the putative NES, site-directed mutations that cause substitutions of conserved NES-A residues were first selected to identify hypermorphic alleles. Next, a portable Crm1p-binding NES from HIV-1 Rev protein that functions in yeast was fused en masse to the C-terminus of variant Upf3 proteins using loxP sites recognized by bacterial cre-recombinase. Finally, variant Upf3-Rev proteins that were functional in NMD were selected and examined for the types of amino acid substitutions present in NES-A. The mutational analysis revealed that amino acid substitutions in the Upf3 NES impair both nuclear export and the Upf2p-Upf3p interaction, both of which are required for Upf3p to function in NMD. The method described in this report could be modified for the genetic analysis of a variety of portable protein domains

Insights into the Function of the CRM1 Cofactor RanBP3 from the Structure of Its Ran-Binding Domain

Proteins bearing a leucine-rich nuclear export signal (NES) are exported from the nucleus by the transport factor CRM1, which forms a cooperative ternary complex with the NES-bearing cargo and with the small GTPase Ran. CRM1-mediated export is regulated by RanBP3, a Ran-interacting nuclear protein. Unlike the related proteins RanBP1 and RanBP2, which promote disassembly of the export complex in the cytosol, RanBP3 acts as a CRM1 cofactor, enhancing NES export by stabilizing the export complex in the nucleus. RanBP3 also alters the cargo selectivity of CRM1, promoting recognition of the NES of HIV-1 Rev and of other cargos while deterring recognition of the import adaptor protein Snurportin1. Here we report the crystal structure of the Ran-binding domain (RBD) from RanBP3 and compare it to RBD structures from RanBP1 and RanBP2 in complex with Ran and CRM1. Differences among these structures suggest why RanBP3 binds Ran with unusually low affinity, how RanBP3 modulates the cargo selectivity of CRM1, and why RanBP3 promotes assembly rather than disassembly of the export complex. The comparison of RBD structures thus provides an insight into the functional diversity of Ran-binding proteins

Are psychosocial interventions effective in reducing alcohol consumption during pregnancy and motherhood?:A systematic review and meta‐analysis

Background and Aims Alcohol use by pregnant and parenting women can have serious and long-lasting consequences for both the mother and offspring. We reviewed the evidence for psychosocial interventions to reduce maternal drinking. Design Literature searches of PsycINFO, PubMed and Scopus identified randomised controlled trials of interventions with an aim of reduced drinking or abstinence in mothers or pregnant women. Setting Interventions were delivered in healthcare settings and homes. Participants Pregnant women and mothers with dependent children. Interventions Psychosocial interventions were compared with usual care or no intervention. Measurements The revised Cochrane risk-of-bias tool for randomised trials was used for quality assessments. Narrative synthesis summarised the findings of the studies with a subset of trials eligible for random-effects meta-analysis. General and alcohol-specific behaviour change techniques (BCTs) were identified to investigate potential mechanism of change. Results Twenty-four studies were included (20 pregnancy, four motherhood). Because of quality of reporting, data from only six pregnancy and four motherhood studies could be pooled. A significant treatment effect was revealed by the meta-analyses of pregnancy studies regarding abstinence (OR = 2.31, 95% CI = 1.61, 3.32; P < 0.001) and motherhood studies regarding a reduction in drinking (standardised mean difference [SMD] = −0.20, 95% CI = −0.38, −0.02; P = 0.03). Narrative synthesis of the remaining trials yielded inconsistent results regarding intervention effectiveness. A wide range of BCTs were used, present in both effective and ineffective interventions. The most commonly used general and alcohol-specific BCTs included information about consequences, social support, goal setting and action planning. Conclusions In pregnant women identified as consuming alcohol, psychosocial interventions appear to increase abstinence rates compared with usual care or no intervention. Similarly, such interventions appear to lead to a reduction in alcohol consumption in mothers with dependent children. It is unclear that behaviour change techniques are contributing to these effects. Conclusions from randomised controlled trials are only meaningful if the behavioural outcome, population, setting, intervention and comparator are clearly reported. An important barrier when it comes to identifying effective behaviour change techniques is a widespread failure to provide enough information in study reports

Nuclear Import and Export Signals of Human Cohesins SA1/STAG1 and SA2/STAG2 Expressed in Saccharomyces cerevisiae

Abstract Background: Human SA/STAG proteins, homologues of the yeast Irr1/Scc3 cohesin, are the least studied constituents of the sister chromatid cohesion complex crucial for proper chromosome segregation. The two SA paralogues, SA1 and SA2, show some specificity towards the chromosome region they stabilize, and SA2, but not SA1, has been shown to participate in transcriptional regulation as well. The molecular basis of this functional divergence is unknown. Methodology/Principal Findings: In silico analysis indicates numerous putative nuclear localization (NLS) and export (NES) signals in the SA proteins, suggesting the possibility of their nucleocytoplasmic shuttling. We studied the functionality of those putative signals by expressing fluorescently tagged SA1 and SA2 in the yeast Saccharomyces cerevisiae. Only the Nterminal NLS turned out to be functional in SA1. In contrast, the SA2 protein has at least two functional NLS and also two functional NES. Depending on the balance between these opposing signals, SA2 resides in the nucleus or is distributed throughout the cell. Validation of the above conclusions in HeLa cells confirmed that the same N-terminal NLS of SA1 is functional in those cells. In contrast, in SA2 the principal NLS functioning in HeLa cells is different from that identified in yeast and is localized to the C-terminus. Conclusions/Significance: This is the first demonstration of the possibility of non-nuclear localization of an SA protein. The reported difference in the organization between the two SA homologues may also be relevant to their partially divergent functions. The mechanisms determining subcellular localization of cohesins are only partially conserved between yeast and human cells