Genome sequence of enterohaemorrhagic Escherichia coli O157:H7

The bacterium Escherichia coli O157:H7 is a worldwide threat to public health and has been implicated in many outbreaks of haemorrhagic colitis, some of which included fatalities caused by haemolytic uraemic syndrome. Close to 75,000 cases of O157:H7 infection are now estimated to occur annually in the United States. The severity of disease, the lack of effective treatment and the potential for large-scale outbreaks from contaminated food supplies have propelled intensive research on the pathogenesis and detection of E. coli O157:H7 (ref. 4). Here we have sequenced the genome of E. coli O157:H7 to identify candidate genes responsible for pathogenesis, to develop better methods of strain detection and to advance our understanding of the evolution of E. coli, through comparison with the genome of the non-pathogenic laboratory strain E. coli K-12 (ref. 5). We find that lateral gene transfer is far more extensive than previously anticipated. In fact, 1,387 new genes encoded in strain-specific clusters of diverse sizes were found in O157:H7. These include candidate virulence factors, alternative metabolic capacities, several prophages and other new functions--all of which could be targets for surveillance.     

Genome-wide association and linkage identify modifier loci of lung disease severity in cystic fibrosis at 11p13 and 20q13.2

A combined genome-wide association and linkage study was used to identify loci causing variation in cystic fibrosis lung disease severity. We identified a significant association (P = 3.34 × 10(-8)) near EHF and APIP (chr11p13) in p.Phe508del homozygotes (n = 1,978). The association replicated in p.Phe508del homozygotes (P = 0.006) from a separate family based study (n = 557), with P = 1.49 × 10(-9) for the three-study joint meta-analysis. Linkage analysis of 486 sibling pairs from the family based study identified a significant quantitative trait locus on chromosome 20q13.2 (log(10) odds = 5.03). Our findings provide insight into the causes of variation in lung disease severity in cystic fibrosis and suggest new therapeutic targets for this life-limiting disorder.     

Membrane interiorization by phagocytosing macrophages — an ultrastructural morphometric approach

Summary Stereological methods have been used to quantify selected membrane compartments of normal and activated rat peritoneal macrophages, before and after phagocytosis of latex beads. Despite being rounder, activated cells are more efficient phagocytes: 30 min after latex challenge they suffer a greater nett depletion of plasma membrane and sequester more and larger phagocytic vacuoles. However, phagocytosis of latex is not the major route of membrane interiorization.We wish to thank Professor R. Barer for his advice and criticism. The work was undertaken by L.O. as a research project in partial fulfilment of requirements for a B.Sc. degree in Human Biology and Anatomy, University of Sheffield.     

Key residues involved in calcium-binding motifs in EGF-like domains

Many extracellular proteins with diverse functions contain domains similar to epidermal growth factor (EGF), a number of which have a consensus Asp/Asn, Asp/Asn, Asp*/Asn*, Tyr/Phe (where the asterisk denotes a beta-hydroxylated residue). These include the coagulation factors IX and X, proteins with two EGF-like domains, the first of which contains the consensus residues. The first EGF-like domain of human factor IX contains a calcium-binding site, which is believed to be responsible for one of the high-affinity sites detected in this protein. Similar results have been obtained for bovine factor X. We have now used protein engineering and 1H-NMR techniques to investigate the importance of individual consensus residues for ligand binding. Measurement of a calcium-dependent Tyr 69 shift in the isolated first EGF-like domain from human factor IX demonstrates that Asp 47, Asp 49, and Asp 64 are directly involved in this binding. Gln 50, whose importance has previously been overlooked, is also involved in this binding. Two mutations in this domain, Asp 47----Glu, and Asp 64----Asn, present in patients with haemophilia B, reduce calcium binding to the domain greater than 4-fold and greater than 1,000-fold, respectively. Furthermore, the defective calcium binding of Asn 64 can be partially rescued by the compensatory mutation Gln 50----Glu. This latter mutation, when introduced singly more than doubles the affinity of the domain for calcium. This study thus defines residues involved in a new type of calcium-binding site and provides strong circumstantial evidence for calcium-binding motifs in many extracellular proteins, including the developmentally important proteins of Drosophila, notch, delta and crumbs.     

Quantitative ultrastructural features of maturing mononuclear phagocytes in rat peritoneal fluids.

Ultrastructural features of the in vivo transformation of macrophage congeners in resident and adjuvant-induced peritoneal populations are evaluated by sterological methods. Maturation involves an increase in cell size by the differential hypertrophy of subcellular compartments, notably remaining cytoplasm, nucleus and lysosome-like granules. Larger cells have more and larger granules, more mitochondria and a greater plasmalemmal surface. In contrast, adjuvant activation tends to produce fewer granules and a nett loss of surface membrane.     

Vertical disparity pooling and the induced effect

If the image received by one eye is vertically magnified by a small amount then an illusory tilt is perceived around the vertical axis through the fixation point. This is known as the induced effect and it can be explained by a recent computational theory of binocular vision which treats it as a side-effect of the use of vertical disparities to recover information about the distance to the fixation point and the angle of gaze. We have investigated the consequences of introducing vertical magnifications of some parts of a scene and not others and report here that there is a simple linear relationship between the size of the induced effect and the average vertical magnification. This suggests that a pooling strategy is adopted in the measurement of vertical disparities, a result which fits in well with expectations of the theory.