Alba-domain proteins of Trypanosoma brucei are cytoplasmic RNA-binding proteins that interact with the translation machinery

Trypanosoma brucei and related pathogens transcribe most genes as polycistronic arrays that are subsequently processed into monocistronic mRNAs. Expression is frequently regulated post-transcriptionally by cis-acting elements in the untranslated regions (UTRs). GPEET and EP procyclins are the major surface proteins of procyclic (insect midgut) forms of T. brucei. Three regulatory elements common to the 3' UTRs of both mRNAs regulate mRNA turnover and translation. The glycerol-responsive element (GRE) is unique to the GPEET 3' UTR and regulates its expression independently from EP. A synthetic RNA encompassing the GRE showed robust sequence-specific interactions with cytoplasmic proteins in electromobility shift assays. This, combined with column chromatography, led to the identification of 3 Alba-domain proteins. RNAi against Alba3 caused a growth phenotype and reduced the levels of Alba1 and Alba2 proteins, indicative of interactions between family members. Tandem-affinity purification and co-immunoprecipitation verified these interactions and also identified Alba4 in sub-stoichiometric amounts. Alba proteins are cytoplasmic and are recruited to starvation granules together with poly(A) RNA. Concomitant depletion of all four Alba proteins by RNAi specifically reduced translation of a reporter transcript flanked by the GPEET 3' UTR. Pulldown of tagged Alba proteins confirmed interactions with poly(A) binding proteins, ribosomal protein P0 and, in the case of Alba3, the cap-binding protein eIF4E4. In addition, Alba2 and Alba3 partially cosediment with polyribosomes in sucrose gradients. Alba-domain proteins seem to have exhibited great functional plasticity in the course of evolution. First identified as DNA-binding proteins in Archaea, then in association with nuclear RNase MRP/P in yeast and mammalian cells, they were recently described as components of a translationally silent complex containing stage-regulated mRNAs in Plasmodium. Our results are also consistent with stage-specific regulation of translation in trypanosomes, but most likely in the context of initiation.

A sublimation technique for high-precision measurements of d13CO2 and mixing ratios of CO2 and N2O from air trapped in ice cores

In order to provide high precision stable carbon isotope ratios (δ13CO2 or δ13C of CO2) from small bubbly, partially and fully clathrated ice core samples we developed a new method based on sublimation coupled to gas chromatography-isotope ratio mass spectrometry (GC-IRMS). In a first step the trapped air is quantitatively released from ~30 g of ice and CO2 together with N2O are separated from the bulk air components and stored in a miniature glass tube. In an off-line step, the extracted sample is introduced into a helium carrier flow using a minimised tube cracker device. Prior to measurement, N2O and organic sample contaminants are gas chromatographically separated from CO2. Pulses of a CO2/N2O mixture are admitted to the tube cracker and follow the path of the sample through the system. This allows an identical treatment and comparison of sample and standard peaks. The ability of the method to reproduce δ13C from bubble and clathrate ice is verified on different ice cores. We achieve reproducibilities for bubble ice between 0.05 ‰ and 0.07 ‰ and for clathrate ice between 0.05 ‰ and 0.09 ‰ (dependent on the ice core used). A comparison of our data with measurements on bubble ice from the same ice core but using a mechanical extraction device shows no significant systematic offset. In addition to δ13C, the CO2 and N2O mixing ratios can be volumetrically derived with a precision of 2 ppmv and 8 ppbv, respectively.

Sexual mixing and HIV risk among ethnic minority MSM in Britain

We conducted a cross-sectional online survey of men who have sex with men (MSM) living in Britain in 2007-2008 to examine sexual mixing among ethnic minority MSM. The sample comprised 115 black, 112 South Asian, 47 Chinese and 4,434 white MSM who reported unprotected anal intercourse (UAI) in the previous 3 months. In each ethnic minority group, MSM were three times more likely to report UAI with a partner of the same ethnicity than would be expected by chance alone (χ(2) > 8.43, p < 0.05). Nonetheless, most (>80 %) ethnic minority MSM reported UAI with men from an ethnic group other than their own. In multivariable analysis there was statistical evidence that, compared with white British MSM, self-reported HIV seropositivity remained low for South Asian and Chinese MSM after adjusting for UAI with partners of the same ethnicity (e.g. South Asian MSM, adjusted odds ratio 0.35, 95 % CI 0.19-0.66). This analysis suggests that differences in self-reported HIV seropositivity between ethnic minority and white MSM in Britain cannot be explained by sexual mixing with partners from the same ethnic group.

Continuous measurements of methane mixing ratios from ice cores

This work presents a new, field-deployable technique for continuous, high-resolution measurements of methane mixing ratios from ice cores. The technique is based on a continuous flow analysis system, where ice core samples cut along the long axis of an ice core are melted continuously. The past atmospheric air contained in the ice is separated from the melt water stream via a system for continuous gas extraction. The extracted gas is dehumidified and then analyzed by a Wavelength Scanned-Cavity Ring Down Spectrometer for methane mixing ratios. We assess the performance of the new measurement technique in terms of precision (±0.8 ppbv, 1σ), accuracy (±8 ppbv), temporal (ca. 100 s), and spatial resolution (ca. 5 cm). Using a firn air transport model, we compare the resolution of the measurement technique to the resolution of the atmospheric methane signal as preserved in ice cores in Greenland. We conclude that our measurement technique can resolve all climatically relevant variations as preserved in the ice down to an ice depth of at least 1980 m (66 000 yr before present) in the North Greenland Eemian Ice Drilling ice core. Furthermore, we describe the modifications, which are necessary to make a commercially available spectrometer suitable for continuous methane mixing ratio measurements from ice cores.

Caregiver Responses to the Language Mixing of a Young Trilingual

The situation once described by Hoffmann (1985), in which children grow up exposed to three languages from an early age, is a reality for an increasing number of families. In Europe – as elsewhere – greater mobility is leading to greater numbers of mixed-language couples (Piller 2002), and, by extension, multilingual families. For such families, questions concerning the acquisition and maintenance of three or more languages in a natural environment are of direct relevance. Researchers in bilingualism have already pointed out the importance of social context for the acquisition of two languages in childhood, focusing in particular on the quantity and quality of exposure to the languages (De Houwer 1990; Döpke 1992; Okita 2002; Lanza 2004) or the prestige of the languages (Lambert 1977). In this paper, I will make use of the insights gained by such researchers and test them in a trilingual setting. The paper will focus mainly on one aspect, namely the conversational style of parents and caretakers. The data come from research being carried out in Switzerland and consist of 33 interviews with multilingual families, as well as case studies of two trilingual children. The findings attest to the importance of conversational style, but at the same time indicate that a number of further factors are also of great significance.