Crystallization and preliminary X-ray investigation of Escherichia coli porphobilinogen deaminase.

Porphobilinogen deaminase, the polymerase that catalyses the synthesis of preuroporphyrinogen, the linear tetrapyrrole precursor of uroporphyrinogen III, has been crystallized from sodium acetate buffer with polyethylene glycol 6000 as precipitant. The crystals are orthorhombic and the space group is P2(1)2(1)2, with unit cell dimensions a = 88.01 A, b = 75.86 A, c = 50.53 A and alpha = beta = gamma = 90 degrees, indicating a single molecule of 34 kDa in the asymmetric unit. The crystals grow to dimensions of 1 mm x 2 mm x 0.5 mm within two weeks in the dark and are stable in the X-ray beam for at least 40 hours. Diffraction data beyond 1.7 A resolution, observed with a synchrotron radiation source, indicate that a high resolution structure analysis is feasible.     

Polymorphisms in the human XPD (ERCC2) gene, DNA repair capacity and cancer susceptibility: an appraisal

Using the human XPD (ERCC2) gene as an example, we evaluate the suggestion that polymorphisms in DNA repair genes lead to decreased DNA repair capacity and to increased cancer susceptibility. This intuitively appealing idea provides the rationale for a large number of studies that have attracted much attention from scientists, clinicians and the general public. Unfortunately, most of this work presupposes that a functional effect has been established for the DNA repair gene polymorphisms under study. For XPD, there is no credible evidence for any effect on DNA repair of the two common polymorphisms leading to p.D312N and p.K751Q amino acid variations, and evolutionary analyses strongly predict that both polymorphisms are benign. Current evidence suggests no causal relationship between XPD polymorphisms, reduced DNA repair and increased cancer risk. We do not believe that more studies of the same kind will be useful. Instead, we suggest a combination of several other approaches, which up to now have been used in only a sporadic way, to examine more rigorously the possibility that phenotypic differences are associated with polymorphisms in other DNA repair genes.     

Elastin overexpression by cell-based gene therapy preserves matrix and prevents cardiac dilation

After a myocardial infarction, thinning and expansion of the fibrotic scar contribute to progressive heart failure. The loss of elastin is a major contributor to adverse extracellular matrix remodelling of the infarcted heart, and restoration of the elastic properties of the infarct region can prevent ventricular dysfunction. We implanted cells genetically modified to overexpress elastin to re‐establish the elastic properties of the infarcted myocardium and prevent cardiac failure. A full‐length human elastin cDNA was cloned, subcloned into an adenoviral vector and then transduced into rat bone marrow stromal cells (BMSCs). In vitro studies showed that BMSCs expressed the elastin protein, which was deposited into the extracellular matrix. Transduced BMSCs were injected into the infarcted myocardium of adult rats. Control groups received either BMSCs transduced with the green fluorescent protein gene or medium alone. Elastin deposition in the infarcted myocardium was associated with preservation of myocardial tissue structural integrity (by birefringence of polarized light; P < 0.05 versus controls). As a result, infarct scar thickness and diastolic compliance were maintained and infarct expansion was prevented (P < 0.05 versus controls). Over a 9‐week period, rats implanted with BMSCs demonstrated better cardiac function than medium controls; however, rats receiving BMSCs overexpressing elastin showed the greatest functional improvement (P < 0.01). Overexpression of elastin in the infarcted heart preserved the elastic structure of the extracellular matrix, which, in turn, preserved diastolic function, prevented ventricular dilation and preserved cardiac function. This cell‐based gene therapy provides a new approach to cardiac regeneration.     

Review of elevated atmospheric CO2 effects on agro-ecosystems: residue decomposition processes and soil C storage

A series of studies using major crops (cotton [Gossypium hirsutum L.], wheat [Triticum aestivum L.], grain sorghum [Sorghum bicolor (L.) Moench.] and soybean [Glycine max (L.) Merr.]) were reviewed to examine the impact of elevated atmospheric CO₂ on crop residue decomposition within agro-ecosystems. Experiments evaluated utilized plant and soil material collected from CO₂ study sites using Free Air CO₂ Enrichment (FACE) and open top chambers (OTC). A incubation study of FACE residue revealed that CO₂-induced changes in cotton residue composition could alter decomposition processes, with a decrease in N mineralization observed with FACE, which was dependent on plant organ and soil series. Incubation studies utilizing plant material grown in OTC considered CO₂-induced changes in relation to quantity and quality of crop residue for two species, soybean and grain sorghum. As with cotton, N mineralization was reduced with elevated CO₂ in both species, however, difference in both quantity and quality of residue impacted patterns of C mineralization. Over the short-term (14 d), little difference was observed for CO₂ treatments in soybean, but C mineralization was reduced with elevated CO₂ in grain sorghum. For longer incubation periods (60 d), a significant reduction in CO₂-C mineralized per g of residue added was observed with the elevated atmospheric CO₂ treatment in both crop species. Results from incubation studies agreed with those from the OTC field observations for both measurements of short-term CO₂ efflux following spring tillage and the cumulative effect of elevated CO₂ (> 2 years) in this study. Observations from field and laboratory studies indicate that with elevated atmospheric CO₂, the rate of plant residue decomposition may be limited by N and the release of N from decomposing plant material may be slowed. This indicates that understanding N cycling as affected by elevated CO₂ is fundamental to understanding the potential for soil C storage on a global scale. This revised version was published online in June 2006 with corrections to the Cover Date.     

Hybridization and Back-Crossing in Giant Petrels (Macronectes giganteus and M. halli) at Bird Island,South Georgia,and a Summary of Hybridization in Seabirds

Hybridization in natural populations provides an opportunity to study the evolutionary processes that shape divergence and genetic isolation of species. The emergence of pre-mating barriers is often the precursor to complete reproductive isolation. However, in recently diverged species, pre-mating barriers may be incomplete, leading to hybridization between seemingly distinct taxa. Here we report results of a long-term study at Bird Island, South Georgia, of the extent of hybridization, mate fidelity, timing of breeding and breeding success in mixed and conspecific pairs of the sibling species, Macronectes halli (northern giant petrel) and M. giganteus (southern giant petrel). The proportion of mixed-species pairs varied annually from 0.4–2.4% (mean of 1.5%), and showed no linear trend with time. Mean laying date in mixed-species pairs tended to be later than in northern giant petrel, and always earlier than in southern giant petrel pairs, and their breeding success (15.6%) was lower than that of conspecific pairs. By comparison, mixed-species pairs at both Marion and Macquarie islands always failed before hatching. Histories of birds in mixed-species pairs at Bird Island were variable; some bred previously or subsequently with a conspecific partner, others subsequently with a different allospecific partner, and some mixed-species pairs remained together for multiple seasons. We also report the first verified back-crossing of a hybrid giant petrel with a female northern giant petrel. We discuss the potential causes and evolutionary consequences of hybridization and back-crossing in giant petrels and summarize the incidence of back-crossing in other seabird species.     

The vertical leap ofCercopithecus aethiops sabaeus: Biomechanics and anatomy

In this study, one positional mode, the vertical leap, is selected from the larger repertoire of habitual behaviors of whichCercopithecus aethiops sabaeus is capable, and is quantitatively analyzed. A cinematographic biomechanical analysis of the vertical leap provides a view of the kinematics (time-space properties of the leap) as well as the kinetics (or force properties) of the leap. These are then discussed with regard to anatomical potential. The analysis elucidates three distinct phases of motion during which the moving body segments linked via their connecting joints, affect one another in the production of the leap. The total positional adaptation ofC. a. sabaeus may only be determined after similar analyses are performed for all postural and locomotor modes. The present detailed analysis of vertical leaping is intended to present data for this one positional mode found to be of primary importance in the arboreal environment and in moving from the ground into the trees. In addition a methodology is illustrated for application in similar primate positional studies. A version of this paper was presented at the 43rd Annual Meeting of the American Association of Physical Anthropologists (March, 1974). This research was partially supported by Sigma Xi Grant-in-Aid of Research, Behavioral Science Foundation Fellowship.     

Factors reducing and promoting the effectiveness of proline as an osmoprotectant in Escherichia coli K12

Proline accumulation in Escherichia coli is mediated by three proline porters. Proline catabolism is effected by proline porter I (PPI) and proline/delta 1-pyrroline carboxylate dehydrogenase. Proline did not accumulate cytoplasmically when E. coli was subjected to osmotic stress in minimal salts medium. Although PPI is induced when proline is provided as carbon or nitrogen source, its activity decreased following growth of the bacteria in minimal salts medium of high osmotic strength. Proline dehydrogenase was induced by proline in low or high osmotic strength media. Proline porter II (PPII) was both activated and induced in osmotically stressed bacteria, though the dependencies of the two responses on medium osmolarity differed. Osmotic downshift during the transport measurement decreased the uptake of proline, serine and glutamine by bacteria cultured in media of high osmotic strength. Thus, while osmotic upshift caused specific activation of PPII, osmotic downshift caused a non-specific reduction in amino acid uptake. Glycine betaine inhibited the uptake of [14C]proline via PPII and PPIII but not via PPI. The dependence of that inhibition on glycine betaine concentration was similar when PPII was uninduced, induced or activated by osmotic stress, or induced by amino acid limited growth. Thus PPII and PPIII, not PPI, contribute to the mechanism of osmoprotection by proline and glycine betaine. The tendency for exogenous proline to accumulate in the cytoplasm of bacteria exposed to osmotic stress would, however, be countered by increased proline catabolism.