Excited state intramolecular proton transfer in 3-hydroxy flavone and 5-hydroxy flavone: A DFT based comparative study

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 3-hydroxy-flavone (3HF) and 5-hydroxy-flavone (5HF) were studied using DFT/B3LYP (6-31G (d,p)) and TD-DFT/B3LYP (6-31G (d,p)) level of theory respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Calculated PE curves of 3HF for the ground and excited singlet states proton transfer process explain its four state laser diagram. Excited states PE calculations support the ESIPT process to both 5HF and 3HF. The difference in ESIPT emission process of 3HF and 5HF have been explained in terms of HOMO and LUMO electron distribution of the enol and keto tautomer of these two compounds.     

Centromere identity: a challenge to be faced

The centromere is a genetic locus, required for faithful chromosome segregation, where spindle fibers attach to the chromosome through kinetochore. Loss of centromere or formation of multiple centromeres on a single chromosome leads to chromosome missegregation or chromosome breakage, respectively, which are detrimental for fitness and survival of a cell. Therefore, understanding the mechanism of centromere locus determination on the chromosome and perpetuation of such a locus in subsequent generation (known as centromere identity) is very fundamental to combat conditions like aneuploidy, spontaneous abortion, developmental defects, cell lethality and cancer. Recent studies have come up with different models to explain centromere identity. However, the exact mechanism still remains elusive. It has been observed that most eukaryotic centromeres are determined epigenetically rather than by a DNA sequence. The epigenetic marks that are instrumental in determining centromere identity are the histone H3 variant, CENP-A and the specialized posttranslational modification of the core histones. Here we will review the recent studies on the factors responsible for generating unique centromeric chromatin and how it perpetuates during cell division giving the present-day models. We will further focus on the probable mechanism of de novo centromere formation with an example of neocentromere. As a matter of similitude, this review will include marking extrachromosomal chromatin to be served as a partitioning locus by deposition of CENP-A homolog in budding yeast.     

Obesity and Receipt of Clinical Preventive Services in Veterans

Although obese individuals utilize health care at higher rates than their normal weight counterparts, they may be less likely to receive certain preventive services. We conducted a retrospective cohort study of veterans with visits to 136 national Veterans Affairs (VA) outpatient clinics in the United States in the year 2000. The cohort included 1,699,219 patients: 94% men, 48% white, and 76% overweight or obese. Overweight and obese patients had higher adjusted odds of receiving each of the targeted clinical preventive services as recommended over 5 years compared with normal weight patients. The odds for receiving vaccinations increased linearly with BMI category: influenza (men: odds ratio (OR) = 1.13 for overweight to OR = 1.42 for obese class 3; women: OR = 1.15 for overweight to OR = 1.61 for obese class 3) and pneumococcus (men: OR = 1.02 for overweight to OR = 1.15 for obese class 3; women: OR = 1.08 for overweight to OR = 1.28 for obese class 3). The odds for receiving the cancer screening services typically peaked in the mild‐moderately obese categories. The highest OR for prostate cancer screening was in obese class 2 (OR = 1.29); for colorectal cancer, obese class 1 (men: OR = 1.15; women OR = 1.10); for breast cancer screening, obese class 2 (OR = 1.19); and for cervical cancer screening, obese class 2 (OR = 1.06). In a large national sample, obese patients received preventive services at higher, not lower, rates than their normal weight peers. This may be due to the VA health service coverage and performance directives, a more homogeneous patient demographic profile, and/or unmeasured factors related to service receipt.     

Eclipse-synchrony relationship in Escherichia coli strains with mutations affecting sequestration, initiation of replication and superhelicity of the bacterial chromosome

Initiation of replication from oriC on the Escherichia coli chromosomes occurs once and only once per generation at the same cell mass per origin. During rapid growth there are overlapping replication cycles, and initiation occurs synchronously at two or more copies of oriC. Since the bacterial growth can vary over a wide range (from three divisions per hour to 2.5 hours or more per division) the frequency of initiation should change in coordination with bacterial growth. Prevention of reinitiation from a newly replicated origin by temporary sequestration of the hemi-methylated GATC-sites in the origin region provides the molecular/genetic basis for the maintenance of the eclipse period between two successive rounds of replication. Sequestration is also believed to be responsible for initiation synchrony, since inactivation of either the seqA or the dam gene abolishes synchrony while drastically reducing the eclipse. In this work, we attempted to examine the functional relationship(s) between the eclipse period and the synchrony of initiation in E.coli strains by direct measurements of these parameters by density-shift centrifugation and flow-cytometric analyses, respectively. The eclipse period, measured as a fraction of DNA-duplication times, varied continuously from 0.6 for the wild-type E.coli K12 to 0.1 for strains with mutations in seqA, dam, dnaA, topA and gyr genes (all of which have been shown to cause asynchrony) and their various combinations. The asynchrony index, a quantitative indicator for the loss of synchrony of initiation, changed from low (synchronous) to high (asynchronous) values in a step-function-like relationship with the eclipse. An eclipse period of approximately 0.5 generation time appeared to be the critical value for the switch from synchronous to asynchronous initiation.     

Environmental isolates of Aeromonas spp. harboring the cagA-like gene of Helicobacter pylori

We investigated the presence of cagA-like gene of Helicobacter pylori in environmental isolates of Aeromonas spp. from different water samples of Calcutta, India, by colony hybridization using a cagA-specific DNA probe and by PCR with cagA-specific primers. Nucleotide sequencing of five PCR products revealed 97 to 98% homology to canonical cagA of H. pylori 26695 as well as to four clinical H. pylori strains from Calcutta. The cagA-like gene of the environmental isolates was unstable in laboratory conditions and tended to be lost upon subculturing.     

Host controlled plasmid replication: Escherichia coli minichromosomes

Escherichia coli minichromosomes are plasmids replicating exclusively from a cloned copy of oriC, the chromosomal origin of replication. They are therefore subject to the same types of replication control as imposed on the chromosome. Unlike natural plasmid replicons, minichromosomes do not adjust their replication rate to the cellular copy number and they do not contain information for active partitioning at cell division. Analysis of mutant strains where minichromosomes cannot be established suggest that their mere existence is dependent on the factors that ensure timely once per cell cycle initiation of replication. These observations indicate that replication initiation in E. coli is normally controlled in such a way that all copies of oriC contained within the cell, chromosomal and minichromosomal, are initiated within a fairly short time interval of the cell cycle. Furthermore, both replication and segregation of the bacterial chromosome seem to be controlled by sequences outside the origin itself.     

Construction and characterization of a soybean yeast artificial chromosome library and identification of clones for the<Emphasis Type="Italic"> Rps6</Emphasis> region

We report the construction and characterization of the first soybean yeast artificial chromosome (YAC) library using high-molecular weight DNA isolated from leaf nuclei of the cultivar Conrad 94 that carries Phytophthora resistance genes Rps1-k and Rps6. The quality of this library has been evaluated through analysis of 393 randomly selected YAC clones. The library consists of 36,864 clones, of which 19,956 carry single soybean YACs with an average size of about 285 kb. The library represents approximately five soybean genome equivalents. The probability of finding any soybean sequences from this library is about 0.99. The library was screened for 43 SSR markers representing the whole soybean genome. We were able to identify positive YAC pools for 95% of the SSR markers. Two YAC clones carrying molecular markers linked to the Rps6 gene were identified. The YAC library reported here would be a useful resource for map-based cloning of agronomically important soybean genes and also to complement the effort towards construction of the physical map for the soybean genome.     

Inheritance of inter-simple-sequence-repeat polymorphisms and linkage with a fusarium wilt resistance gene in chickpea

 The inheritance of an inter-simple-sequence-repeat (ISSR) polymorphism was studied in a cross of cultivated chickpea (Cicer arietinum L.) and a closely related wild species (C. reticulatum Lad.) using primers that anneal to a simple repeat of various lengths, sequences and non-repetitive motifs. Dinucleotides were the majority of those tested, and provided all of the useful banding patterns. The ISSR loci showed virtually complete agreement with expected Mendelian ratios. Twenty two primers were used for analysis and yielded a total of 31 segregating loci. Primers based on (GA)_n repeats were the most abundant while primers with a (TG)_n repeat gave the largest number of polymorphic loci. Nucleotides at the 5′ and 3′ end of the primers played an important role in detecting polymorphism. All the markers showed dominance. We found an ISSR marker linked to the gene for resistance to fusarium wilt race 4. The marker concerned, UBC-855₅₀₀, was found to be linked in repulsion with the fusarium wilt resistance gene at a distance of 5.2 cM. It co-segregated with CS-27₇₀₀, a RAPD marker previously shown to be linked to the gene for resistance to fusarium wilt race 1, and was mapped to linkage group 6 of the Cicer genome. This indicated that genes for resistance to fusarium wilt races 1 and 4 are closely linked. The marker UBC-855₅₀₀ is located 0.6 cM from CS-27₇₀₀ and is present on the same side of the wilt resistance gene. To our knowledge this is the first report of the utility of an ISSR marker in gene tagging. These markers may provide valuable information for the development of sequence-tagged microsatellite sites (STMS) at a desired locus. Received: 10 August 1997 / Accepted: 6 October 1997