The guanine-hypoxanthine permease GhxP of Erwinia amylovora facilitates the influx of the toxic guanine derivative 6-thioguanine.

AIM: Erwinia amylovora is the causal agent of fire blight, a devastating disease of apples and pears. This study determines whether the E. amylovora guanine-hypoxanthine transporter (EaGhxP) is required for virulence and if it can import the E. amylovora produced toxic analogue 6-thioguanine (6TG) into cells. METHODS AND RESULTS: Characterization of EaGhxP in guanine transport deficient Escherichia coli reveals that it can transport guanine, hypoxanthine and the toxic analogues 8-azaguanine (8AG) and 6TG. Similarly, EaGhxP transports 8AG and 6TG into E. amylovora cells. EaGhxP has a high affinity for 6TG with a Ki of 3·7 µmol l-1 . An E. amylovora ⊿ghxP::Camr strain shows resistance to growth on 8AG and 6TG. Although EaGhxP is expressed during active disease propagation, it is not necessary for virulence as determined on immature apple and pear assays. CONCLUSIONS: EaGhxP is not required for virulence, but it does import 6TG into E. amylovora cells. SIGNIFICANCE AND IMPACT OF THE STUDY: As part of the disease establishment process, E. amylovora synthesizes and exports a toxic guanine derivative 6TG. Our results are counter intuitive and show that EaGhxP, an influx transporter, can move 6TG into cells raising questions regarding the role of 6TG in disease establishment.

Adrenergic signaling in human oral keratinocytes and wound repair.

Catecholamines are present in saliva, but their influence on oral epithelium is not understood. Because psychological stress increases salivary catecholamines and impairs oral mucosal wound healing, we sought to determine if epithelial adrenergic signaling could link these two findings. We found that cultured human oral keratinocytes (HOK) express the α(2B)- and ß(2)-adrenergic receptors (ARs). Exposure of HOK to either epinephrine or the ß-AR agonist, isoproterenol, reduced migratory speed and decreased in vitro scratch wound healing. Incubation with the ß-AR antagonist timolol reversed the catecholamine-induced effects, indicating that the observed response is mediated by ß-AR. Epinephrine treatment decreased phosphorylation of the mitogen-activated protein kinases (MAPK) ERK1/2 and p38; these decreases were also reversed with timolol. Cultured HOK express enzymes of the epinephrine synthetic pathway, and generate epinephrine. These findings demonstrate that stress-induced elevations of salivary catecholamines signal through MAPK pathways, and result in impaired oral keratinocyte migration required for healing.

IntAct--open source resource for molecular interaction data.

IntAct is an open source database and software suite for modeling, storing and analyzing molecular interaction data. The data available in the database originates entirely from published literature and is manually annotated by expert biologists to a high level of detail, including experimental methods, conditions and interacting domains. The database features over 126,000 binary interactions extracted from over 2100 scientific publications and makes extensive use of controlled vocabularies. The web site provides tools allowing users to search, visualize and download data from the repository. IntAct supports and encourages local installations as well as direct data submission and curation collaborations. IntAct source code and data are freely available from http://www.ebi.ac.uk/intact.

A comparison of Australian and Canadian calibration coefficients for air kerma and absorbed dose to water for 60Co gamma radiation.

Australian and Canadian calibration coefficients for air kerma and absorbed dose to water for 60Co gamma radiation have been compared using transfer standard ionization chambers of types NE 2561 and NE 2611A. Whilst the primary standards of air kerma are similar, both being thick-walled graphite cavity chambers but employing different methods to evaluate the Awall correction, the primary standards of absorbed dose to water are quite different. The Australian standard is based on measurements made with a graphite calorimeter, whereas the Canadian standard uses a sealed water calorimeter. The comparison result, expressed as a ratio of calibration coefficients R=N(ARPANSA)/N(NRC), is 1.0006 with a combined standard uncertainty of 0.35% for the air kerma standards and 1.0052 with a combined standard uncertainty of 0.47% for the absorbed dose to water standards. This demonstrates the agreement of the Australian and Canadian radiation dosimetry standards. The results are also consistent with independent comparisons of each laboratory with the BIPM reference standards. A 'trilateral' analysis confirms the present determination of the relationship between the standards, within the 0.09% random component of the combined standard uncertainty for the three comparisons.

A survey of blood lead levels among young Johannesburg school children.

Studies conducted around the world have established beyond doubt that elevated childhood blood lead levels may lead to detrimental health effects. Research has shown that certain groups of South African children are at particular risk of elevated blood lead levels. Johannesburg is the largest urban complex in southern Africa, with a population of around 3 million and extensive industrial and manufacturing activity. Among the challenges posed in the city are rapid urbanization, extensive poverty, and inequity. Little information on the blood lead distribution of Johannesburg children is available. This study was undertaken to determine blood lead levels among children living in three areas of Johannesburg: inner city suburbs and the low-income townships of Alexandra and Westbury to the north and west of the city center, respectively. The results indicated that blood lead levels ranged from 6 to 26 micro g/dL, with a mean level of 11.9 micro g /dL. The blood lead levels of 78% of children equaled or exceeded 10 micro g/dL, the current international action level. Maternal educational status, the presence of smokers in the home, and living in an informal dwelling were among the factors associated with elevated blood lead levels.

The relative response of NE2561 and NE2611A ionization chambers in megavoltage x-ray beams.

The relative energy response of NE2561 and NE261 IA ionization chambers to megavoltage photon beams from the ARPANSA linac indicates significant differences between these two types of chamber. In 16 MV beams of TPR20(10) 0.779, differences of about 2% are observed. The results are expressed as ratios KQ of the beam quality correction factors kQ, where the kQ factor for each type of chamber is the ratio of the absorbed dose to water calibration factor ND, at the x-ray quality Q to that at 60Co. These results have implications for the use of generic kQ factors in dosimetry protocols and suggest that NE2561 and NE2611A ionization chambers cannot be assumed to be identical.

Impact of depressive symptoms on hospitalization risk in community-dwelling older persons.

OBJECTIVE: To determine whether depressive symptoms in older adults are associated with an increased risk for hospitalization. DESIGN: A 6 month cohort study. SETTING: Five counties in the northern Piedmont of North Carolina from the Duke University site of the Established Populations for Epidemiological Studies of the Elderly project. PARTICIPANTS: The sample included 3486 community-dwelling adults, aged 65 and older. MEASUREMENTS: Crude risk ratios for the effect of depressive symptoms on 6 month risk for hospitalization were calculated, followed by a multivariable analysis controlling for demographics and health status. RESULTS: Three hundred participants were hospitalized during the 6 month follow-up period. The crude risk ratio for the effect of depressive symptoms on hospitalization was 1.95 (95% CI = 1.47-2.58). Subgroup analysis showed significant positive risk ratios for men aged 65 to 74 and > or =75, and women aged 65 to 74. After a multivariable analysis, however, these associations remained significant only among men > or =75 (RR = 3.43; 95% CI = 1.33-8.86). CONCLUSIONS: Depressive symptoms were independently associated with a more than threefold increased risk for hospitalization among men aged > or =75. This result reflects differences in the effects of depressive symptoms across age and gender groups, and emphasizes that symptoms of depression influence overall health and medical utilization among, at the very least, the oldest subset of men.

The 1998 Australian external beam radiotherapy survey and IAEA/WHO TLD postal dose quality audit.

The results of an updated Australian survey of external beam radiotherapy centres are presented. Most of the centres provided most of the requested information. The relative caseloads of various linear accelerator photon and electron beams have not changed significantly since the previous survey in 1995. The mean age of Australian LINACs is 7.1 years and that of other radiotherapy machines is 14.7 years. Every Australian radiotherapy centre participated in a special run of the IAEA/WHO TLD postal dose quality audit program, which was provided for Australian centres by the IAEA and WHO in May 1998. The dose quoted by the centres was in nearly every case within 1.5% of the dose assessed by the IAEA. This is within the combined standard uncertainty of the IAEA TLD service (1.8%). The results confirm the accuracy and precision of radiotherapy dosimetry in Australia and the adequate dissemination of the Australian standards from ARL (now ARPANSA) to the centres. The Australian standards have recently been shown to agree with those of other countries to within 0.25% by comparison with the BIPM.

The plant cell cycle.

Molecular controls of the plant cell cycle must integrate environmental signals within developmental contexts. Recent advances highlight the fundamental conservation of underlying cell cycle mechanisms between animals and plants, overlaid by a rich molecular and regulatory diversity that is specific to plant systems. Here we review plant cell cycle regulators and their control.

Cytokinin activation of Arabidopsis cell division through a D-type cyclin.

Cytokinins are plant hormones that regulate plant cell division. The D-type cyclin CycD3 was found to be elevated in a mutant of Arabidopsis with a high level of cytokinin and to be rapidly induced by cytokinin application in both cell cultures and whole plants. Constitutive expression of CycD3 in transgenic plants allowed induction and maintenance of cell division in the absence of exogenous cytokinin. Results suggest that cytokinin activates Arabidopsis cell division through induction of CycD3 at the G1-S cell cycle phase transition.

The maize retinoblastoma protein homologue ZmRb-1 is regulated during leaf development and displays conserved interactions with G1/S regulators and plant cyclin D (CycD) proteins.

Recent discoveries of plant retinoblastoma (Rb) protein homologues and D-type cyclins suggest that control of the onset of cell division in plants may have stronger parallels with mammalian G1/S controls than with yeasts. In mammals, the Rb protein interacts specifically with D-type cyclins and regulates cell proliferation by binding and inhibiting E2F transcription factors. However, the developmental role of Rb in plants and its potential interaction with cell cycle regulators is unknown. We show that the maize Rb homologue ZmRb-1 is temporally and spatially regulated during maize leaf development. ZmRb-1 is highly expressed in differentiating cells, but almost undetectable in proliferating cells. In vitro, both ZmRb-1 and human Rb bind all classes of plant D-type cyclins with the involvement of a conserved N-terminal Leu-x-Cys-x-Glu (LxCxE) Rb-interaction motif. This binding is strongly reduced by mutation of the conserved Cys-470 of ZmRb-1. ZmRb-1 binds human and Drosophila E2F, and inhibits transcriptional activation of human E2F. We also show that ZmRb-1 is a good in vitro substrate for all human G1/S protein kinases. The functional conservation of proteins that control the G1/S transition in mammals and plants points to the existence of plant E2F homologues. We conclude that evolution of Rb and cyclin D proteins occurred after separation of the fungi from the higher eukaryotic lineage, but preceded the divergence of plant and animal kingdoms.

Synthesis and confirmation of structure for a new gibberellin, 2 beta-hydroxy-GA12 (GA110), from spinach and oil palm.

The identity of a new gibberellin (GA) in spinach and oil palm sap has been confirmed as 2 beta-hydroxy-GA12 (GA110) by comparisons of GC-mass spectral data obtained for the trimethylsilyl ether methyl ester derivatives with those of a synthetic sample prepared by means of a 24 step sequence from gibberellic acid; 2 beta-hydroxy-GA24 was also prepared. Experimental details for the latter part of the syntheses are described.

Intraoral air pressure of alaryngeal speakers during a no-air insufflation maneuver.

Intraoral air pressure was recorded during the production of the consonant cognate pairs /p/-/b, /t/-/d, and /s/-/z/ by eight esophageal speakers. These consonants were combined with the vowel /a/ to form CV, VCV, and VC syllables and produced under two experimental conditions: after the insufflation of air and without air insufflation. The purpose was to determine if the voiced-voiceless pressure difference associated with the production of cognate pairs would occur in the absence of an insufflated air flow source. The results revealed that peak intraoral air pressure magnitudes were significantly greater following the insufflation of air than without it. Moreover, the voiceless consonants were generally produced with greater peak air pressures than the voiced consonants under both experimental conditions, although not all contrasts were significantly different. Finally, peak air pressure magnitudes were significantly more variable in the air insufflation condition. The finding that the esophageal speakers exhibited a pressure difference relative to voicing in the absence of an insufflated air flow source provides support to the concept that intraoral air pressure may be an important variable in regulating and controlling consonant production.

Intercomparison of the national exposure standards of New Zealand and Australia.

An intercomparison of medium energy x-ray and 60Co gamma radiation exposure standards held by the Australian Radiation Laboratory and the National Radiation Laboratory (New Zealand) is reported. The standards agree within 0.4%.

Reinforced variability in rats: effects of gender, age and contingency.

Operant variability was compared in four groups of Long-Evans rats (young males, young females, mature males and mature females) under two different conditions. Under VAR contingencies, where response variability was required for reinforcement, a sequence of four responses on left (L) and right (R) levers had to differ from each of the preceding four sequences. If LLLL, LRLL, RRRR, and RRLL had just occurred, then a RLRL sequence, for example, would be reinforced in the next trial, but LRLL would not. Sequence variability was compared to that under YOKE contingencies, where reinforcement was provided whether or not the rats varied their responses. We found that young rats behaved more variably than mature rats, this effect most pronounced under the YOKE contingencies, where variability was not required. On the other hand, variability was not related to gender under either VAR or YOKE conditions. Thirdly, all groups were sensitive to the schedule contingencies, behaving more variably under VAR than under YOKE. Thus age and schedule requirements influenced operant variability, but gender did not.

Aging and consonant errors in reverberation and noise.

Identification accuracy and error patterns on the City University of New York (CUNY) Nonsense Syllable Test were examined for three groups of subjects (young normal-hearing, older hearing-impaired, and older with minimal hearing loss) listening binaurally in four conditions (quiet, noise, reverberation, and reverberation plus noise). Percent-correct performance was analyzed for stimuli aggregated by place and manner categories, and error patterns were examined via analysis of variance and correlational procedures. Results suggested that some of the difficulty experienced by the older subjects was related to amount of hearing loss, but a portion of the data could not be explained by elevated auditory thresholds. Confusion patterns also varied across listening conditions, especially for the nasal and semivowel stimuli.

Standards and calibration facilities of the Australian Radiation Laboratory for ionizing radiation beams.

The Australian Radiation Laboratory (ARL) maintains national standards of exposure and working standards of absorbed dose. Some of the exposure standards maintained by ARL have been compared recently with those of the Bureau International des Poids et Mesures (BIPM) for 100 to 250 kV x-rays and 60Co gamma rays. The absorbed dose standard for 60Co gamma rays is compared regularly with other standards through the International Atomic Energy Agency (IAEA) and World Health Organization (WHO). All results show good agreement. A range of calibration qualities is offered at ARL, extending from 10 kV x-rays to 60Co gamma rays. A system of regional facilities has been developed for radiation protection calibrations; each facility is supplied with a set of 137Cs sources and an ionization chamber and electrometer for use with x-rays. The system is now almost complete throughout Australia.

The effectiveness of simultaneous cues on naming disturbance in aphasia.

The effects of increased information redundancy on word retrieval in aphasic patients was investigated in this study. Protocols involved combining five types of cues commonly utilized in aphasia management into eight pairs, each of which could be presented simultaneously. The resulting cue combinations were presented to 16 anterior lesion aphasic subjects who manifested mild to severe word-finding difficulty. All of the combinations were effective in facilitating picture-naming performance, with the severe group demonstrating the most dramatic improvement when simultaneous prompts were utilized. A cueing hierarchy incorporating increased stimulus redundancy is supported.