Directed evolution of rubisco in Escherichia coli reveals a specificity-determining hydrogen bond in the form II enzyme.

Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) occupies a critical position in photosynthetic CO2-fixation and consequently has been the focus of intense study. Crystal-structure-guided site-directed mutagenesis studies have met with limited success in engineering kinetic improvements to Rubisco, highlighting our inadequate understanding of structural constraints at the atomic level that dictate the enzyme's catalytic chemistry. Bioselection provides an alternative random mutagenic approach that is useful for identifying and elucidating imperceptible structure-function relationships.

The catalytic properties of hybrid Rubisco comprising tobacco small and sunflower large subunits mirror the kinetically equivalent source Rubiscos and can support tobacco growth.

Plastomic replacement of the tobacco (Nicotiana tabacum) Rubisco large subunit gene (rbcL) with that from sunflower (Helianthus annuus; rbcL(S)) produced tobacco(Rst) transformants that produced a hybrid Rubisco consisting of sunflower large and tobacco small subunits (L(s)S(t)). The tobacco(Rst) plants required CO(2) (0.5% v/v) supplementation to grow autotrophically from seed despite the substrate saturated carboxylation rate, K(m), for CO(2) and CO(2)/O(2) selectivity of the L(s)S(t) enzyme mirroring the kinetically equivalent tobacco and sunflower Rubiscos.

Implications of cnidarian gene expression patterns for the origins of bilaterality is the glass half full or half empty?

The past two years have seen a dramatic increase in the available data on gene sequence and gene expression for cnidarians and other "lower" Metazoa, and a flurry of recent papers has drawn on these to address the origins of bilaterality. Cnidarian homologs of many genes that play key roles in the specification of both the A/P and D/V axes of bilaterians have been characterized, and their patterns of expression determined. Some of these expression patterns are consistent with the possibility of conservation of function between Cnidaria and Bilateria, but others clearly differ.

Environmental motion delays the detection of movement-based signals.

Animal signals are constrained by the environment in which they are transmitted and the sensory systems of receivers. Detection of movement-based signals is particularly challenging against the background of wind-blown plants. The Australian lizard Amphibolurus muricatus has recently been shown to compensate for greater plant motion by prolonging the introductory tail-flicking component of its movement-based display.

Engineering model proteins for Photosystem II function.

Our knowledge of Photosystem II and the molecular mechanism of oxygen production are rapidly advancing. The time is now ripe to exploit this knowledge and use it as a blueprint for the development of light-driven catalysts, ultimately for the splitting of water into O2 and H2. In this article, we outline the background and our approach to this technological application through the reverse engineering of Photosystem II into model proteins.

Investigation of substrate water interactions at the high-affinity Mn site in the photosystem II oxygen-evolving complex.

18 O isotope exchange measurements of photosystem II (PSII) in thylakoids from wild-type and mutant Synechocystis have been performed to investigate binding of substrate water to the high-affinity Mn4 site in the oxygen-evolving complex (OEC). The mutants investigated were D1-D170H, a mutation of a direct ligand to the Mn4 ion, and D1-D61N, a mutation in the second coordination sphere. The substrate water 18 O exchange rates for D61N were found to be 0.

Photoactivatable GFP resolves Drosophila mesoderm migration behaviour.

Mesoderm migration is a pivotal event in the early embryonic development of animals. One of the best-studied examples occurs during Drosophila gastrulation. Here, mesodermal cells invaginate, undergo an epithelial-to-mesenchymal transition (EMT), and spread out dorsally over the inner surface of the ectoderm.

Differences in carbon isotope discrimination of three variants of D-ribulose-1,5-bisphosphate carboxylase/oxygenase reflect differences in their catalytic mechanisms.

The carboxylation kinetic (stable carbon) isotope effect was measured for purified d-ribulose-1,5-bisphosphate carboxylases/oxygenases (Rubiscos) with aqueous CO(2) as substrate by monitoring Rayleigh fractionation using membrane inlet mass spectrometry. This resulted in discriminations (Delta) of 27.4 +/- 0.

Infection process and the interaction of rice roots with rhizobia.

Most rhizobial strains inhibit rice root growth in the presence of calcium or potassium nitrates, but not ammonium nitrate. Certain rhizobial strains, however, such as strain R4, do not inhibit rice growth and can enter rice roots and multiply in the intercellular spaces. By using the green fluorescent protein (GFP) as a visual marker, it was found that Rhizobium became intimately associated with rice seedling roots within 24-48 h.

The effect of parental rearing conditions on offspring life history in Anopheles stephensi.

Background: The environmental conditions experienced by parents are increasingly recognized to impact the success of offspring. Little is known on the presence of such parental effects in Anopheles. If present, parental effects could influence mosquito breeding programmes, some malaria control measures and have epidemiological and evolutionary consequences.

Estimating the dielectric constant of the channel protein and pore.

When modelling biological ion channels using Brownian dynamics (BD) or Poisson-Nernst-Planck theory, the force encountered by permeant ions is calculated by solving Poisson's equation. Two free parameters needed to solve this equation are the dielectric constant of water in the pore and the dielectric constant of the protein forming the channel. Although these values can in theory be deduced by various methods, they do not give a reliable answer when applied to channel-like geometries that contain charged particles.

Brownian dynamics theory for predicting internal and external blockages of tetraethylammonium in the KcsA potassium channel.

The theory of Brownian dynamics is used to model permeation and the blocking of KcsA potassium channels by tetraethylammonium (TEA). A novel Brownian dynamics simulation algorithm is implemented that comprises two free energy profiles; one profile is seen by the potassium ions and the other by the TEA molecules whose shape is approximated by a sphere. Our simulations reveal that internally applied TEA blocks the passage of K(+) ions by physically occluding the pore.

The fiddler crab Uca mjoebergi uses colour vision in mate choice.

Although the role of colour in mate choice is well known, few tests of colour vision have been based on mating behaviour. Females of the fiddler crab Uca mjoebergi have recently been shown to use claw coloration to recognize conspecific males. In this study I demonstrate that the females use colour vision for this task; preferentially approaching yellow claws over grey claws regardless of their intensity while failing to discriminate between yellow claws differing in intensity.

Flavonoids are differentially taken up and transported long distances in Arabidopsis.

Flavonoids are synthesized in response to developmental and environmental signals and perform many functions in plants. Arabidopsis (Arabidopsis thaliana) roots grown in complete darkness do not accumulate flavonoids since the expression of genes encoding enzymes of flavonoid biosynthesis is light dependent. Yet, flavonoids accumulate in root tips of plants with light-grown shoots and light-shielded roots, consistent with shoot-to-root flavonoid movement.

Influence of adapting speed on speed and contrast coding in the primary visual cortex of the cat.

Adaptation is a ubiquitous property of the visual system. Adaptation often improves the ability to discriminate between stimuli and increases the operating range of the system, but is also associated with a reduced ability to veridically code stimulus attributes. Adaptation to luminance levels, contrast, orientation, direction and spatial frequency has been studied extensively, but knowledge about adaptation to image speed is less well understood.

Construction and evolution of imprinted loci in mammals.

Genomic imprinting first evolved in mammals around the time that humans last shared a common ancestor with marsupials and monotremes (180-210 million years ago). Recent comparisons of large imprinted domains in these divergent mammalian groups have shown that imprinting evolved haphazardly at various times in different lineages, perhaps driven by different selective forces. Surprisingly, some imprinted domains were formed relatively recently, using non-imprinted components acquired from unexpected genomic regions.

A new look at the evolution of avian sex chromosomes.

Birds have a ubiquitous, female heterogametic, ZW sex chromosome system. The current model suggests that the Z chromosome and its degraded partner, the W chromosome, evolved from an ancestral pair of autosomes independently from the mammalian XY male heteromorphic sex chromosomes--which are similar in size, but not gene content (Graves, 1995; Fridolfsson et al., 1998).

Analysis of carboxysomes from Synechococcus PCC7942 reveals multiple Rubisco complexes with carboxysomal proteins CcmM and CcaA.

In cyanobacteria, the key enzyme for photosynthetic CO(2) fixation, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), is bound within proteinaceous polyhedral microcompartments called carboxysomes. Cyanobacteria with Form IB Rubisco produce beta-carboxysomes whose putative shell proteins are encoded by the ccm-type genes. To date, very little is known of the protein-protein interactions that form the basis of beta-carboxysome structure.

Sensors, motors, and tuning in the cochlea: interacting cells could form a surface acoustic wave resonator.

The outer hair cells of the cochlea occur in three distinct and geometrically precise rows and, unusually, display both sensing and motor properties. As well as sensing sound, outer hair cells (OHCs) undergo cycle-by-cycle length changes in response to stimulation. OHCs are central to the way in which the cochlea processes and amplifies sounds, but how they do so is presently unknown.

δC of organic matter transported from the leaves to the roots in Eucalyptus delegatensis: short-term variations and relation to respired CO.

Post-photosynthetic carbon isotope fractionation might alter the isotopic signal imprinted on organic matter (OM) during primary carbon fixation by Rubisco. To characterise the influence of post-photosynthetic processes, we investigated the effect of starch storage and remobilisation on the stable carbon isotope signature (δC) of different carbon pools in the Eucalyptus delegatensis R. T.

Origin and evolution of spermatogenesis genes on the human sex chromosomes.

Both the X and Y chromosomes have a remarkable enrichment of genes involved in gonadogenesis and gametogenesis. The small Y chromosome contains the sex determining gene SRY, as well as many genes that are critical for spermatogenesis and are expressed exclusively in the testis. The X chromosome, too, is enriched for genes involved in sex and reproduction.

Relationship between mitochondrial DNA damage and photoreceptor death in developing and adult retina, assessed in normal and degenerative rat strains.

In this study, we used Real-Time PCR to study the correlation of mtDNA deletions and photoreceptor death by apoptosis in one normal (SD) and two different degenerative (RCS and P23H) rat strains. Our results show that, in the SD and RCS strains, mtDNA deletion frequency increased and fell during neonatal life, correlating with rates of photoreceptor death during the critical period of photoreceptor development, and into adulthood. Results suggest that mitochondrial damage occurs in close association with photoreceptor death, in the normal (SD) and fast degenerative (RCS) retinas.

Cytoskeleton and cell wall function in penetration resistance.

Plants successfully repel the vast majority of potential pathogens that arrive on their surface, with most microorganisms failing to breach the outer epidermal wall. Resistance to penetration at the epidermis is a key component of basal defence against disease and critically depends on fortification of the cell wall at the site of attempted penetration through the development of specialised cell wall appositions rich in antimicrobial compounds. Formation of cell wall appositions is achieved by rapid reorganisation of actin microfilaments, actin-dependent transport of secretory products to the infection site and local activation of callose synthesis.

New roads lead to Rubisco in archaebacteria.

The discovery of the CO(2)-fixing enzyme Rubisco in the Archaebacteria has presented a conundrum in that they apparently lack the gene for phosphoribulokinase, which is required to generate Rubisco's substrate ribulose 1,5-bisphosphate (RuBP). However, two groups have now demonstrated novel RuBP synthesis pathways, demystifying Rubisco's non-autotrophic and perhaps ancient role. A new CO(2) fixing role for Rubisco, which is distinct from the globally dominant Calvin cycle, is providing important clues furthering our understanding of the evolution of autotrophy.