Plasmodium knowlesi, a malaria parasite originally thought to be restricted to macaques in Southeast Asia, has recently been recognized as a significant cause of human malaria. Unlike the benign and ...morphologically similar P. malariae, these parasites can lead to fatal infections. Malaria parasites, including P. knowlesi, have not yet been detected in macaques of the Kapit Division of Malaysian Borneo, where the majority of human knowlesi malaria cases have been reported. In order to extend our understanding of the epidemiology and evolutionary history of P. knowlesi, we examined 108 wild macaques for malaria parasites and sequenced the circumsporozoite protein (csp) gene and mitochondrial (mt) DNA of P. knowlesi isolates derived from macaques and humans. We detected five species of Plasmodium (P. knowlesi, P. inui, P. cynomolgi, P. fieldi and P. coatneyi) in the long-tailed and pig-tailed macaques, and an extremely high prevalence of P. inui and P. knowlesi. Macaques had a higher number of P. knowlesi genotypes per infection than humans, and some diverse alleles of the P. knowlesi csp gene and certain mtDNA haplotypes were shared between both hosts. Analyses of DNA sequence data indicate that there are no mtDNA lineages associated exclusively with either host. Furthermore, our analyses of the mtDNA data reveal that P. knowlesi is derived from an ancestral parasite population that existed prior to human settlement in Southeast Asia, and underwent significant population expansion approximately 30,000-40,000 years ago. Our results indicate that human infections with P. knowlesi are not newly emergent in Southeast Asia and that knowlesi malaria is primarily a zoonosis with wild macaques as the reservoir hosts. However, ongoing ecological changes resulting from deforestation, with an associated increase in the human population, could enable this pathogenic species of Plasmodium to switch to humans as the preferred host.
Background
The relative age effect (RAE) is a worldwide phenomenon, allowing sport participation and elite selection to be based on birthdate distribution. Negative consequences include both a ...narrow, non-optimal elite selection and negative health effects on entire populations. This study investigated the RAE and athletic performance in multiple individual sports in Sweden.
Methods
Birthdates of athletes born between the years 1922 and 2015 were collected across 4-month periods (tertiles: T1, T2, T3) from cross-country skiing (
N
= 136,387), orienteering (
N
= 41,164), athletics (
N
= 14,503), alpine skiing (
N
= 508), E-sports (
N
= 47,030), and chess (
N
= 4889). In total, data from 244,560 athletes (women:
N
= 79,807, men:
N
= 164,753) was compared to the complete parent population of 5,390,954 births in Sweden during the same years. Chi-squared statistics compared parent and cohort distributions stratified by sport, sex, and age.
Results
A significantly skewed distribution of birthdates was present in all sports, both sexes, and most age groups. The largest RAEs are seen in children where T1 often constitutes 40–50% and T3, 20–25% of the population. In E-sports, an inversed RAE was seen in adults. In most investigated sports, birthdate distribution was correlated to performance in children but not in adults.
Conclusions
Skewed birthdate distributions were consistently prevalent in all investigated individual sports in Sweden, both physically demanding and cognitive/skill-based. As sport participation is related to total level of physical activity, both present and future, failing to address the RAE issue at an early age will result not only in a narrow and arbitrary selection for adult elite athletes but also in a negative impact on public health.
The mechanism by which double-strand DNA breaks are repaired in the radiation-resistant bacterium
Deinococcus radiodurans is not well understood. This organism lacks the RecBCD helicase/nuclease, ...which processes broken DNA ends in other bacteria. The RecF pathway is an alternative pathway for recombination and DNA repair in
E. coli, when RecBCD is absent due to mutation, and
D. radiodurans may rely on enzymes of this pathway for double-strand break repair. The RecJ exonuclease is thought to process broken DNA ends for the RecF pathway. We attempted to delete the
recJ gene from
D. radiodurans, using homologous recombination to replace the gene with a streptomycin-resistance cassette. We were unable to obtain a complete deletion mutant, in which the gene is deleted from all of the chromosome copies in this polyploid organism. Quantitative real-time PCR shows that the heterozygous mutants have a
recJ gene copy that is
ca. 10–30% that of the wild-type. Mutants with reduced
recJ gene copy grow slowly and are more sensitive than wild-type to UV irradiation, gamma irradiation, and hydrogen peroxide. The mutants are as resistant as wild-type to methyl-methanesulfonate. The
D. radiodurans RecJ protein was expressed in
E. coli and purified under denaturing conditions. The re-folded protein has nuclease activity on single-stranded DNA with specificity similar to that of
E. coli RecJ exonuclease.
The bacterium Deinococcus radiodurans is extremely resistant to high levels of DNA-damaging agents, including gamma rays and ultraviolet light that can lead to double-stranded DNA breaks. ...Surprisingly, the organism does not appear to have a RecBCD enzyme, an enzyme that is critical for double-strand break repair in many other bacteria. The D. radiodurans genome does encode a protein whose closest characterized homologues are RecD subunits of RecBCD enzymes in other bacteria. We have purified this novel D. radiodurans RecD protein and characterized its biochemical activities. The D. radiodurans RecD protein is a DNA helicase that unwinds short (20 base pairs) DNA duplexes with either a 5'-single-stranded tail or a forked end, but not blunt-ended or 3'-tailed duplexes. Duplexes with 10-12 nucleotide (nt) 5'-tails are good unwinding substrates and are bound tightly, while DNA with shorter tails (4-8 nt) are poor unwinding substrates and are bound much less tightly. The RecD protein is much less efficient at unwinding slightly longer substrates (52 or 76 base pairs, with 12 nt 5'-tails). Unwinding of the longer substrates is stimulated somewhat (4-5-fold) by the single-stranded DNA-binding protein from D. radiodurans. These results show that the D. radiodurans RecD protein is a DNA helicase with 5'-3' polarity and low processivity.
The RecBCD enzyme from Escherichia coli is an ATP-dependent helicase and an ATP-stimulated nuclease. The 3′→ 5′exonuclease activity on double-stranded DNA is suppressed when the enzyme encounters a ...recombinational hot spot, called chi (χ ). We have prepared a RecB deletion mutant (RecB1-929) by using results of limited proteolysis experiments that indicated that the RecB subunit consists of two main domains. The RecB1-929protein, comprising the 100-kDa N-terminal domain of RecB, is an ATP-dependent helicase and a single-stranded DNA-dependent ATPase. Reconstitution of RecB1-929with RecC and RecD leads to processive unwinding of a linearized plasmid. However, the reconstituted RecB1-929CD enzyme has lost the single-strand endo- and exonuclease and the double-strand exonuclease activities of the RecBCD enzyme. These results show that the 30-kDa C-terminal domain of RecB has an important role in the nuclease activity of RecBCD. On the basis of these findings, we propose the RecB C-terminal domain swing model to explain RecBCD's transformation from a 3′→ 5′exonuclease to a helicase when it meets a χ site.
Deinococcus radiodurans survives extremely high doses of ionizing and ultraviolet radiation and treatment with various DNA-damaging chemicals. As an effort to identify and characterize proteins that ...function in DNA repair in this organism, we have studied the protein encoded by locus DR1572. This gene is predicted to encode a Superfamily I DNA helicase, except that genome sequencing indicated that it has a one-base frameshift and would not encode a complete helicase. We have cloned the gene from two different
D. radiodurans strains and find that the frameshift mutation is not present. The corrected gene encodes a 755 residue protein that is similar to the
Bacillus subtilis YvgS protein and to helicase IV of
Escherichia coli. The purified protein (helicase IV
Dr) has ATP hydrolysis and DNA helicase activity. A truncated protein that lacks 214 residues from the N-terminus, which precede the conserved helicase domain, has greater ATPase activity than the full-length protein but has no detectable helicase activity. Disruption of locus DR1572 in the
D. radiodurans chromosome causes greater sensitivity to hydrogen peroxide and methyl-methanesulfonate compared to wild-type cells, but no change in resistance to gamma and ultraviolet radiation and to mitomycin C. The results indicate that locus DR1572 encodes a complete protein that contributes to DNA metabolism in
D. radiodurans.
Some Differences Make a Difference Jackson, Susan E; Brett, Joan F; Sessa, Valerie I ...
Journal of applied psychology,
10/1991, Letnik:
76, Številka:
5
Journal Article
Recenzirano
Schneider's (1987)
attraction-selection-attrition model and
Pfeffer's (1983)
organization demography model were used to generate individual-level and group-level hypotheses relating interpersonal ...context to recruitment, promotion, and turnover patterns. Interpersonal context was operationalized as personal dissimilarity and group heterogeneity with respect to age, tenure, education level, curriculum, alma mater, military service, and career experiences. For 93 top management teams in bank holding companies examined over a 4-yr period, turnover rate was predicted by group heterogeneity. For individuals, turnover was predicted by dissimilarity to other group members, but promotion was not. Team heterogeneity was a relatively strong predictor of team turnover rates. Furthermore, reliance on internal recruitment predicted subsequent team homogeneity.
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