Hysteresis response of daytime net ecosystem exchange during drought

Continuous measurements of net ecosystem CO<sub>2</sub> exchange (NEE) using the eddy-covariance method were made over an agricultural ecosystem in the southeastern US. During optimum environmental conditions, photosynthetically active radiation (PAR) was the primary driver controlling daytime NEE, accounting for as much as 67 to 89% of the variation in NEE. However, soil water content became the dominant factor limiting the NEE-PAR response during the peak growth stage. NEE was significantly depressed when high PAR values coincided with very low soil water content. The presence of a counter-clockwise hysteresis of daytime NEE with PAR was observed during periods of water stress. This is a result of the stomatal closure control of photosynthesis at high vapor pressure deficit and enhanced respiration at high temperature. This result is significant since this hysteresis effect limits the range of applicability of the Michaelis-Menten equation and other related expressions in the determination of daytime NEE as a function of PAR. The systematic presence of hysteresis in the response of NEE to PAR suggests that the gap-filling technique based on a non-linear regression approach should take into account the presence of water-limited field conditions. Including this step is therefore likely to improve current evaluation of ecosystem response to increased precipitation variability arising from climatic changes

Synthesis of oligodeoxyribonucleotides containing a tricyclic thio analogue of O6-methylguanine and their recognition by MGMT and Atl1

Promutagenic O6-alkylguanine adducts in DNA are repaired in humans by O6-methylguanine-DNA-methyltransferase (MGMT) in an irreversible reaction. Here we describe the synthesis of a phosphoramidite that allows the preparation of oligodeoxyribonucleotides (ODNs) containing a novel tricyclic thio analogue of O6-methylguanine in which the third ring bridges the 6-thio group and C7 of a 7-deazapurine. These ODNs are very poor substrates for MGMT and poorly recognised by the alkyltransferase-like protein, Atl1. Examination of the active sites of both MGMT and Atl1 suggest large steric clashes hindering binding of the analogue. Such analogues, if mutagenic, are likely to be highly toxic

Association of arterial stiffness with single nucleotide polymorphism rs1333049 and metabolic risk factors

The electronic version of this article is the complete one and can be found online at: http://www.cardiab.com/content/12/1/93. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.BACKGROUND: Increased arterial stiffness is a cardiovascular outcome of metabolic syndrome (MetS). The chromosome 9p21 locus has been identified as a major locus for risk of coronary artery disease (CAD). The single nucleotide polymorphism (SNP), rs1333049 on chromosome 9p21.3 has been strongly associated with CAD and myocardial infarction. Increased arterial stiffness could be the link between the 9p21 polymorphism and increased cardiovascular risk. Since the impact of a genetic polymorphism on arterial stiffness especially in Asian populations has not been well defined, we aimed to investigate the association of arterial stiffness with rs 1333049 variant on chromosome 9p21.3 in Thai subjects with and without MetS risk factors. METHODS: A total of 208 Thai subjects, aged 35-75 years, 135 with and 73 without MetS, according to IDF and NCEP-ATPIII criteria, were included in this study. Aortic-femoral pulse wave velocity (afPWV), brachial-ankle pulse wave velocity (baPWV) and aortic ankle pulse wave velocity (aaPWV) were measured and used as markers of arterial stiffness. The chromosome 9p21.3 locus, represented by the rs 1333049 variant and blood biochemistry were evaluated. RESULTS: Arterial stiffness was elevated in subjects with MetS when compared with nonMetS subjects. PWV, especially afPWV increased progressively with increasing number of MetS risk factors (r = 0.322, P <0.001). We also found that the frequency distribution of the rs1333049 genotypes is significantly associated with the afPWV (P <0.05). In multivariate analyses, there was an association between homozygous C allele and afPWV (Odds ratio (OR), 8.16; 95% confidence interval (CI), 1.91 to 34.90; P = 0.005), while the GC genotype was not related to afPWV (OR, 1.79; 95% CI, 0.84 to 3.77; P = 0.129) when compared with the GG genotype. CONCLUSIONS: Our findings demonstrate for the first time that arterial stiffness is associated with genetic polymorphism in 9p21 and metabolic risk factors in a Thai population

Atl1 Regulates Choice between Global Genome and Transcription-Coupled Repair of O6-Alkylguanines

Nucleotide excision repair (NER) has long been known to remove DNA lesions induced by chemical carcinogens, and the molecular mechanism has been partially elucidated. Here we demonstrate that in Schizosaccharomyces pombe a DNA recognition protein, alkyltransferase-like 1 (Atl1), can play a pivotal role in selecting a specific NER pathway, depending on the nature of the DNA modification. The relative ease of dissociation of Atl1 from DNA containing small O6-alkylguanines allows accurate completion of global genome repair (GGR), whereas strong Atl1 binding to bulky O6-alkylguanines blocks GGR, stalls the transcription machinery, and diverts the damage to transcription-coupled repair. Our findings redraw the initial stages of the NER process in those organisms that express an alkyltransferase-like gene and raise the question of whether or not O6-alkylguanine lesions that are poor substrates for the alkyltransferase proteins in higher eukaryotes might, by analogy, signal such lesions for repair by NER

Mass spectrometric analysis of the active site tryptic peptide of recombinant O6-methylguanine-DNA methyltransferase following incubation with human colorectal DNA reveals the presence of an O6-alkylguanine adductome

Human exposure to DNA alkylating agents is poorly characterized, partly because only a limited range of specific alkyl DNA adducts have been quantified. The human DNA repair protein, O6-methylguanine O6-methyltransferase (MGMT), irreversibly transfers the alkyl group from DNA O6-alkylguanines (O6-alkGs) to an acceptor cysteine, allowing the simultaneous detection of multiple O6-alkG modifications in DNA by mass spectrometric analysis of the MGMT active site peptide (ASP). Recombinant MGMT was incubated with oligodeoxyribonucleotides (ODNs) containing different O6-alkGs, Temozolomide-methylated calf thymus DNA (Me-CT-DNA), or human colorectal DNA of known O6-MethylG (O6-MeG) levels. It was digested with trypsin, and ASPs were detected and quantified by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. ASPs containing S-methyl, S-ethyl, S-propyl, S-hydroxyethyl, S-carboxymethyl, S-benzyl, and S-pyridyloxobutyl cysteine groups were detected by incubating MGMT with ODNs containing the corresponding O6-alkGs. The LOQ of ASPs containing S-methylcysteine detected after MGMT incubation with Me-CT-DNA was <0.05 pmol O6-MeG per mg CT-DNA. Incubation of MGMT with human colorectal DNA produced ASPs containing S-methylcysteine at levels that correlated with those of O6-MeG determined previously by HPLC-radioimmunoassay (r2 = 0.74; p = 0.014). O6-CMG, a putative O6-hydroxyethylG adduct, and other potential unidentified MGMT substrates were also detected in human DNA samples. This novel approach to the identification and quantitation of O6-alkGs in human DNA has revealed the existence of a human DNA alkyl adductome that remains to be fully characterized. The methodology establishes a platform for characterizing the human DNA O6-alkG adductome and, given the mutagenic potential of O6-alkGs, can provide mechanistic information about cancer pathogenesis

Group versus modified individual standard-setting on multiple-choice questions with the Angoff method for fourth-year medical students in the internal medicine clerkship

Vichai Senthong,1,* Jarin Chindaprasirt,1,* Kittisak Sawanyawisuth,1 Noppadol Aekphachaisawat,2 Suteeraporn Chaowattanapanit,1 Panita Limpawattana,1 Charoen Choonhakarn,1 Aumkhae Sookprasert1 1Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand; 2Central Library, Silpakorn University, Bangkok, Thailand *These authors contributed equally to this work Background: The Angoff method is one of the preferred methods for setting a passing level in an exam. Normally, group meetings are required, which may be a problem for busy medical educators. Here, we compared a modified Angoff individual method to the conventional group method. Methods: Six clinical instructors were divided into two groups matched by teaching experience: modified Angoff individual method (three persons) and conventional group method (three persons). The passing scores were set by using the Angoff theory. The groups set the scores individually and then met to determine the passing score. In the modified Angoff individual method, passing scores were judged by each instructor and the final passing score was adjusted by the concordance method and reliability index. Results: There were 94 fourth-year medical students who took the test. The mean (standard deviation) test score was 65.35 (8.38), with a median of 64 (range 46&ndash;82). The three individual instructors took 45, 60, and 60 minutes to finish the task, while the group spent 90 minutes in discussion. The final passing score in the modified Angoff individual method was 52.18 (56.75 minus 4.57) or 52 versus 51 from the standard group method. There was not much difference in numbers of failed students by either method (four versus three). Conclusion: The modified Angoff individual method may be a feasible way to set a standard passing score with less time consumed and more independent rather than group work by instructors. Keywords: Angoff, individual, passing score, standard-setting, multiple-choice questions, internal medicin