Ubiquitin genes as a paradigm of concerted evolution of tandem repeats

Summary Ubiquitin is remarkable for its ubiquitous distribution and its extreme protein sequence conservation. Ubiquitin genes comprise direct repeats of the ubiquitin coding unit with no spacers. The nucleotide sequences of several ubiquitin repeats from each of humans, chicken,Xenopus, Drosophila, barley, and yeast have recently been determined. By analysis of these data we show that ubiquitin is evolving more slowly than any other known protein, and that this (together with its gene organization) contributes to an ideal situation for the occurrence of concerted evolution of tandem repeats. By contrast, there is little evidence of between-cluster concerted evolution. We deduce that in ubiquitin genes, concerted evolution involves both unequal crossover and gene conversion, and that the average time since two repeated units within the polyubiquitin locus most recently shared a common ancestor is approximately 38 million years (Myr) in mammals, but perhaps only 11 Myr inDrosophila. The extreme conservatism of ubiquitin evolution also allows the inference that certain synonymous serine codons differing at the first two positions were probably mutated at single steps.     

FIGL1 coordinates with dosage-sensitive BRCA2 in modulating meiotic recombination in maize

Meiotic crossover(CO) formation between homologous chromosomes ensures their subsequent proper segregation and generates genetic diversity among offspring. In maize, however, the mechanisms that modulate CO formation remain poorly characterized. Here, we found that both maize BREAST CANCER SUSCEPTIBILITY PROTEIN 2(BRCA2) and AAA-ATPase FIDGETIN-LIKE-1(FIGL1)act as positive factors of CO formation by controlling the assembly or/and stability of two conserved DNA recombinases RAD51 and DMC1 filame...     

A wide family of pyridoxal thiosemicarbazone ferric complexes: Syntheses, structures and magnetic properties

This study reports the syntheses and the characterization of 12 ferric complexes of pyridoxal thiosemicarbazone. The richness of the coordination chemistry of this ligand is highlighted by the modulation of its charge from neutral H₂L to anionic L²⁻, thus leading to a wide family of ferric compounds with charge varying from +3 to −1. The structures of complexes [Fe(HL)₂]ClO₄ · 2H₂O and [Fe(HL)L] · 4.5H₂O were solved and discussed with a particular attention brought to the intermolecular interactions occurring between the complexes. The investigation of magnetic properties of these compounds revealed that two of them are in the HS state at any temperature, whereas the others are in the LS state. These results are discussed in relation to the modulation of the electronic properties of the ligand.     

Movement between patches, unequal competitors and the ideal free distribution

Researchers have often commented on the ability of the original ideal free distribution (IFD) model to approximate observed animal distributions even though the critical assumption that competitors are of equal ability is usually violated. We provide an explanation by recognizing that animals will occasionally move between patches for reasons other than to simply maximize their resource payoffs, given perfect (i.e. ideal) information about the current payoff in each patch, and that these movements will continue to occur even after an equilibrium is reached. When such movements are incorporated into an unequal competitors IFD model, a single, stable distribution of each competitor type is predicted. This equilibrium will usually be characterized by under-matching of total competitive units relative to the distribution of resources (i.e. too few competitive units in the good patch). More importantly, it will often resemble the original, equal competitors IFD, in that total competitor numbers will come close to matching the distribution of resources. We argue that researchers claiming to have observed an IFD of equal competitors have actually observed this equilibrium distribution of unequal competitors. Our model predicts that the deviation from input-matching will usually be an under-matching of total competitor numbers relative to resources (i.e. too few competitors in the good patch). Examination of published data reveals that post-equilibrium movement between patches occurs frequently and, although the reported distributions are similar to those predicted by input-matching, under-matching is usually observed.     

Genetic Analyses of Meiotic Recombination in Arabidopsis

Meiosis is essential for sexual reproduction and recombination is a critical step required for normal meiosis. Understanding the underlying molecular mechanisms that regulate recombination is important for medical, agricultural and ecological reasons. Readily available molecular and cytological tools make Arabidopsis an excellent system to study meiosis. Here we review recent developments in molecular genetic analyses on meiotic recombination. These include studies on plant homologs of yeast and animal genes, as well as novel genes that were first identified in plants. The characterizations of these genes have demonstrated essential functions from the initiation of recombination by double-strand breaks to repair of such breaks, from the formation of doubie-HoUiday junctions to possible resolution of these junctions, both of which are critical for crossover formation. The recent advances have ushered a new era in plant meiosis, in which the combination of genetics, genomics, and molecular cytology can uncover important gene functions.     

The Biophysical Performance of Argentina (1970–2009)

The biophysical features of the Argentinean economy are examined using a social metabolism approach. A material flow analysis (MFA) for this economy was conducted for the period 1970–2009. Results show that Argentina follows a resource‐intensive and export‐oriented development model with a persistent physical trade deficit. Also, Argentina's terms of trade (the average weight in tonnes of imports that can be purchased through the sale of 1 tonne of exports) show a declining trend in the period of study. Argentina's economy shows a pattern typical of countries whose economies are based primarily on exports. Comparisons between Argentina's metabolic profile and the metabolic profile of other countries in Latin America and of Australia and Spain show that the Argentinean economy presents the same pattern as other Latin American exporting economies, and its terms of trade are opposite to those of industrialized economies.