Lysine methylation within the globular domain of histone H3 by Dot1 is important for telomeric silencing and Sir protein association

The amino-terminal histone tails are subject to covalent post-translational modifications such as acetylation, methylation, and phosphorylation. In the histone code hypothesis, these exposed and unstructured histone tails are accessible to a repertoire of regulatory factors that specifically recognize the various modified histones, thereby generating altered chromatin structures that mediate specific biological responses. Here, we report that lysine (Lys) 79 of histone H3, which resides in the globular domain, is methylated in eukaryotic organisms. In the yeast Saccharomyces cerevisiae, Lys 79 of histone H3 is methylated by Dot1, a protein shown previously to play a role in telomeric silencing. Mutations of Lys 79 of histone H3 and mutations that abolish the catalytic activity of Dot1 impair telomeric silencing, suggesting that Dot1 mediates telomeric silencing largely through methylation of Lys 79. This defect in telomeric silencing might reflect an interaction between Sir proteins and Lys 79, because dot1 and Lys 79 mutations weaken the interaction of Sir2 and Sir3 with the telomeric region in vivo. Our results indicate that histone modifications in the core globular domain have important biological functions.     

Understanding the adaptation of Halobacterium species NRC-1 to its extreme environment through computational analysis of its genome sequence

The genome of the halophilic archaeon Halobacterium sp. NRC-1 and predicted proteome have been analyzed by computational methods and reveal characteristics relevant to life in an extreme environment distinguished by hypersalinity and high solar radiation: (1) The proteome is highly acidic, with a median pI of 4.9 and mostly lacking basic proteins. This characteristic correlates with high surface negative charge, determined through homology modeling, as the major adaptive mechanism of halophilic proteins to function in nearly saturating salinity. (2) Codon usage displays the expected GC bias in the wobble position and is consistent with a highly acidic proteome. (3) Distinct genomic domains of NRC-1 with bacterial character are apparent by whole proteome BLAST analysis, including two gene clusters coding for a bacterial-type aerobic respiratory chain. This result indicates that the capacity of halophiles for aerobic respiration may have been acquired through lateral gene transfer. (4) Two regions of the large chromosome were found with relatively lower GC composition and overrepresentation of IS elements, similar to the minichromosomes. These IS-element-rich regions of the genome may serve to exchange DNA between the three replicons and promote genome evolution. (5) GC-skew analysis showed evidence for the existence of two replication origins in the large chromosome. This finding and the occurrence of multiple chromosomes indicate a dynamic genome organization with eukaryotic character.     

Detection of multiple gene amplifications in glioblastoma multiforme using array-based comparative genomic hybridization

We have used a new method of genomic microarray to investigate amplification of oncogenes throughout the genome of glioblastoma multiforme (GBM). Array-based comparative genomic hybridization (array CGH) allows for simultaneous examination of 58 oncogenes/amplicons that are commonly amplified in various human cancers. Amplification of multiple oncogenes in human cancers can be rapidly determined in a single experiment. Tumor DNA and normal control DNA were labeled by nick translation with green- and red-tagged nucleotides, respectively. Instead of hybridizing to normal metaphase chromosomes in conventional comparative genomic hybridization (CGH), the probes of the mixed fluorescent labeled DNA were applied to genomic array templates comprised of P1, PAC, and BAC clones of 58 target oncogenes. The baseline for measuring deviations was established by performing a series of independent array CGH using test and reference DNA made from normal individuals. In the present study, we examined fourteen GBMs (seven cell lines and seven tumours) with CGH and array CGH to reveal the particular oncogenes associated with this cancer. High-level amplifications were identified on the oncogenes/amplicons CDK4, GLI, MYCN, MYC, MDM2, and PDGFRA. The highest frequencies of gains were detected on PIK3CA (64.3%), EGFR (57.1%), CSE1L (57.1%), NRAS (50%), MYCN (42.9%), FGR (35.7%), ESR (35.7%), PGY1 (35.7%), and D17S167 (35.7%). These genes are suggested to be involved in the GBM tumorigenesis.     

Clonal origin, restricted natural distribution, and conservation of virulence factors in isolates of enterotoxigenic Escherichia coli serogroup O126.

Enterotoxigenic Escherichia coli serogroup O126 isolates have been isolated in Hong Kong since 1982 from sporadic cases of infantile diarrhea and from one outbreak in a neonatal ward. A 64-megadalton plasmid encoding colonization factor antigen I and heat-stable enterotoxin was identified in all 23 isolates. Enterotoxigenic E. coli strains producing heat-stable enterotoxin from different regions of Southeast Asia were collected and compared by biotyping, antibiotic resistance patterns, and plasmid profiles. Restriction endonuclease digestion of plasmids and subsequent Southern blot analysis with the heat-stable enterotoxin gene probe of representative strains showed a unique plasmid was harbored by all heat-stable enterotoxin-producing O126 strains tested. These results are consistent with conservative inheritance of enterotoxin plasmids within enterotoxigenic E. coli strains over a 2-year period in Hong Kong.     

Prosthetic hip joint infection due to Campylobacter fetus.

A case of postoperative prosthetic hip joint infection due to Campylobacter fetus subsp. fetus is described. Difficulties in isolation and antimicrobial susceptibility testing of this organism are discussed.     

Evaluation and optimization of a latex agglutination assay for detection of cholera toxin and Escherichia coli heat-labile toxin.

The effectiveness of a latex agglutination assay kit for the detection of Escherichia coli heat-labile toxin and cholera toxin was determined for the identification of natural isolates of the corresponding enteric pathogens in Southeast Asia. By selection of the appropriate culture media, the sensitivity of the assay was improved from 90.6% (for the detection of heat-labile toxin) and 75% (for the detection of cholera toxin) to 100%, and the results were confirmed with bioassays and DNA hybridization assays for both clinical and environmental isolates.     

Mesh-independent prediction of skin burns injury

This paper presents a robust finite element model (FEM) with multiple-layers of varying properties for investigation of burn effects on human skin during a burning process resulting from exposure of skin surface to a contact heat source and a hot moving fluid. Henriques' theory of skin burns is used in conjunction with two-dimensional Pennes bioheat transfer equation for determining the spatial and temporal extent of burn injury. The model developed is a two-dimensional axisymmetric model in cylindrical coordinates. The various tissue layers account for changing thermal properties with respect to skin anatomy. A finite element scheme that uses the backward Euler method is used to solve the problem. The injury processes of skin subsequent to the removal of the heat source (post-burn) will also be inspected. The mesh employed in this model consists of a high density of nodes and elements in which a thorough mesh convergence study was done. A comparison of the transient temperature field computed by this model against Diller's results using the FE technique with a comparatively coarse mesh of 125 elements and experimental data by Orgill et al. has been done in the present study. It concluded that improved accurate solutions have been performed using the robust model developed due to the achievement of a mesh-independent solution.     

Cytokine production in lethal and non-lethal murine malaria

Levels of IFN-gamma, IL-2 and IL-4 were measured in vitro during the course of non-lethal Plasmodium chabaudi adami and lethal P. chabaudi strain 1309 infections in BALB/cByJ mice. Spleen cells from mice infected with the non-lethal Plasmodium had a higher initial response to P. chabaudi antigens than mice infected with P. chabaudi strain 1309, as determined by measuring all three lymphokines. We conclude that both Th1 and Th2 subsets of T helper lymphocytes are activated during P. chabaudi adami infection but that these responses are suppressed in mice infected with the more virulent P. chabaudi strain 1309.     

Prospective study of community-acquired rotavirus infection.

We determined titers of group A rotavirus common antibodies and neutralizing antibodies against serotypes 1 to 4 of prototype human rotavirus (HRV) in cord blood and serum specimens obtained from 38 infants at 4-month intervals from birth until 2 years of age. Nineteen of the infants developed one episode of HRV diarrhea each, and they were matched by age and birth weight with the other 19 infants, who did not develop HRV diarrhea during the follow-up period. We estimated the incidence rate of HRV infection for the two groups of infants combined to be a minimum of 1.34 episodes per infant per year, which is 22 times more common than the occurrence of overt disease caused by the virus in this community. The infection occurred constantly throughout the first 2 years of infancy, whereas all but one of the 19 episodes of overt disease occurred before 12 months of age. Seven of these overt episodes were preceded by at least one episode of subclinical infection earlier, and the other seven were probably due to primary HRV infection. The remaining five episodes occurred before 4 months of age, so that we could not ascertain whether they were due to primary infections because of the presence of maternal antibodies. We showed that levels of HRV antibodies in serum specimens obtained before clinical onset of diarrhea varied widely, and, for most infants in the diarrheal group, levels of these antibodies were similar to those in the serum specimens obtained at the same times from the corresponding age- and birth weight-matched control infants. Nevertheless, the age at which overt disease caused by HRV was most prevalent coincided with the time when the maternal antibodies had declined to low levels but the infants had not yet acquired high titers of these antibodies in their sera.     

Antigens of virulent and attenuated Rickettsia tsutsugamushi.

We studied the antigens present in L929 mouse fibroblast or rabbit testicular cells, which had been infected or not with a prototype strain of Rickettsia tsutsugamushi, the causal agent of scrub typhus, and its attenuated variant. Immunoblotting revealed four antigens, designated 1, 1a, 2 and 3, which appeared to be specifically associated with infection with this organism. Antigens 1 and 1a had similar mol. wt of about 60 kD and antigen 2 and 3 had mol. wts of 45 kD and 28 kD respectively. Whereas antigen 1a, 2 and 3 were common to infection with either the virulent or the attenuated strains of the organism, antigen 1 was only detected in cells infected with the virulent strain and was reactive only with the antiserum raised against cells infected with that strain. In addition, two antigens were also detected by crossed immunoelectrophoresis, one of which was similarly associated with infection with the virulent strain as antigen 1, while the other was common to infection with either of the strains. It seems that the antigenic cross reaction between the two strains may account, in part at least, for the protection of mice against infection with the virulent strain afforded by the attenuated strain, while the loss or modification of antigen 1 might be associated with attenuation of the organism with respect to its virulence to mice.