Non-equilibrium thermodynamics of Lotka-Volterra ecosystems: Stability and evolution

A non-equilibrium thermodynamic theory of generalized Lotka-Volterra ecosystem has been presented. The main results consist of the derivation of a generalized expression of entropy-production for the evolutionary ecosystem and the study of its role in the analysis of ecological stability, succession and also in the formulation of some extremum principles characterising the evolution of the ecosystem.     

Rapid separation of reduction products of 2,4,6-trinitrotoluene using TLC

Silica gel TLC methods were developed for the separation of 2,4,6-trinitrotoluene (TNT) in mixtures with possible reduction products. The methods employed repeated elutions with simple binary or ternary solvent systems in either one or two dimensional modes. The resolved analytes include TNT, selected amino derivatives (2-amino-4,6-di-nitrotoluene, 4-amino-2,6-dinitrotoluene, 2,4-diamino-6-nitrotoluene) and known hydroxylamino derivatives (2-hydroxyl-amino-4,6-dinitrotoluene, 4-hydroxylamino-2,6-dinitrotoluene and 2,4-dihydroxylamino-6-nitrotoluene).     

Reassessment of the prevalence of heat-stable enterotoxin (NAG-ST) among environmental Vibrio cholerae non-O1 strains isolated from Calcutta, India, by using a NAG-ST DNA probe.

A collection of 521 environmental isolates of Vibrio cholerae which were previously examined by the suckling mouse assay and found to be negative for the heat-stable enterotoxin NAG-ST were reassessed by a recently developed DNA probe for NAG-ST. A total of 12 (2.3%) of the isolates hybridized with the NAG-ST probe. By using a cholera toxin (CT) DNA probe, the CT gene was detected in six of the strains in the collection, although none of the isolates of V. cholerae non-O1 hybridized with both of the toxin probes. All of the NAG-ST and CT probe-positive strains were hemolysin positive. Thirty-fold-concentrated supernatants of the three representative NAG-ST DNA probe-positive V. cholerae non-O1 strains gave positive fluid accumulation ratios in the suckling mouse assay even after heating (100 degrees C for 5 min) and also inhibited the binding of a NAG-ST monoclonal antibody to the bound NAG-ST in a competitive enzyme-linked immunosorbent assay (ELISA). Likewise, all six CT probe-positive V. cholerae non-O1 strains produced in vitro CT when examined by the CT bead ELISA. HindIII digest patterns of chromosomal DNA from the representative NAG-ST gene-positive strains were visually indistinguishable. Between the groups of NAG-ST probe-positive strains examined, there was a variation in the hybridizable fragments, with one group of strains exhibiting a hybridizable fragment similar to that of the NRT 36 reference strain; a smaller HindIII fragment hybridized with the NAG-ST probe in the other group of strains.(ABSTRACT TRUNCATED AT 250 WORDS)     

Multifunctional role for fetuin (fetal protein) in lipid transport.

Recent studies from this laboratory have shown that fetuin 1) is nearly 50-fold more efficient than albumin in incorporating exogenous fatty acids into cultured cells, (JBC, 265: 5883, 1990), and 2) is associated with a lipoprotein-like particle (FASEB J. 3: 2075-2080, 1989). In the present study, this lipid-containing fraction (FLP) was isolated by ultracentrifugation, and its effect on cholesterol efflux from cultured human skin fibroblasts and Hep-G2 cells prelabeled with [14C]cholesterol was investigated. FLP fraction caused a significant efflux of [14C]cholesterol from cells, the same in magnitude as HDL. This effect of fetuin supranatant fraction increased proportionately with concentration and time. Similar results were observed with Hep-G2 cells. This ability to induce efflux of cholesterol was confirmed by a decrease in cholesterol mass of cells after 24 h incubation with FLP. The ultracentrifugal bottom (infranatant) fraction of fetuin (FI) was ineffective in this regard. However, FI was more effective in the incorporation of exogenous fatty acids into cellular triglycerides. These studies suggest that the fetuin molecule is a multifunctional protein (delivery of fatty acids to cells and cholesterol efflux from cells) which may play a role in lipid transport during fetal life.     

How does Sec63 affect the conformation of Sec61 in yeast?

The Sec complex catalyzes the translocation of proteins of the secretory pathway into the endoplasmic reticulum and the integration of membrane proteins into the endoplasmic reticulum membrane. Some substrate peptides require the presence and involvement of accessory proteins such as Sec63. Recently, a structure of the Sec complex from Saccharomyces cerevisiae, consisting of the Sec61 channel and the Sec62, Sec63, Sec71 and Sec72 proteins was determined by cryo-electron microscopy (cryo-EM). Here, we show by co-precipitation that the Sec61 channel subunit Sbh1 is not required for formation of stable Sec63-Sec61 contacts. Molecular dynamics simulations started from the cryo-EM conformation of Sec61 bound to Sec63 and of unbound Sec61 revealed how Sec63 affects the conformation of Sec61 lateral gate, plug, pore region and pore ring diameter via three intermolecular contact regions. Molecular docking of SRP-dependent vs. SRP-independent signal peptide chains into the Sec61 channel showed that the pore regions affected by presence/absence of Sec63 play a crucial role in positioning the signal anchors of SRP-dependent substrates nearby the lateral gate.     

Role of the male specific lethal (msl) genes in modifying the effects of sex chromosomal dosage in Drosophila

Immunostaining of chromosomes shows that the male-specific lethal (MSL) proteins are associated with all female chromosomes at a low level but are sequestered to the X chromosome in males. Histone-4 Lys-16 acetylation follows a similar pattern in normal males and females, being higher on the X and lower on the autosomes in males than in females. However, the staining pattern of acetylation and the mof gene product, a putative histone acetylase, in msl mutant males returns to a uniform genome-wide distribution as found in females. Gene expression on the autosomes correlates with the level of histone-4 acetylation. With minor exceptions, the expression levels of X-linked genes are maintained with either an increase or decrease of acetylation, suggesting that the MSL complex renders gene activity unresponsive to H4Lys16 acetylation. Evidence was also found for the presence of nucleation sites for association of the MSL proteins with the X chromosome rather than individual gene binding sequences. We suggest that sequestration of the MSL proteins occurs in males to nullify on the autosomes and maintain on the X, an inverse effect produced by negatively acting dosage-dependent regulatory genes as a consequence of the evolution of the X/Y sex chromosomal system.     

An Arabidopsis inositol 5-phosphatase gain-of-function alters abscisic acid signaling

Signals can be perceived and amplified at the cell membrane by receptors coupled to the production of a variety of second messengers, including inositol 1,4,5-trisphosphate (IP3). We previously have identified 15 putative inositol 5-phosphatases (5PTases) from Arabidopsis and shown that At5PTase1 can hydrolyze IP3. To determine whether At5PTase1 can terminate IP3-mediated signaling, we analyzed transgenic plants ectopically expressing At5PTase1. Stomata from leaves of At5PTase1 transgenic plants were abscisic acid (ABA) and light insensitive, and ABA induction of genes was delayed. Quantification of IP3 in plants exposed to ABA indicated that ABA induced two IP3 increases in wild-type plants. Both of these IP3 increases were reduced in At5PTase1 transgenic plants, indicating that IP3 may be necessary for stomatal closure and temporal control of ABA-induced gene expression. To determine if ABA could induce expression of At5PTase1, we examined RNA and protein levels of At5PTase1 in wild-type plants exposed to ABA. Our results indicate that At5PTase1 is up-regulated in response to ABA. This is consistent with At5PTase1 acting as a signal terminator of ABA signaling.     

Genomic diversity among Vibrio cholerae O139 strains isolated in Bangladesh and India between 1992 and 1998

In order to assess the extent of genomic diversity among Vibrio cholerae O139 strains, restriction fragment length polymorphisms in two genetic loci, rrn and ctx, were studied. Analysis of 144 strains isolated from different regions of Bangladesh and India between 1992 and 1998 revealed the presence of at least six distinct ribotypes (B-I through B-VI) of which three were new ribotypes, and one of these was represented by a nontoxigenic O139 strain. Strains of ribotypes B-I through B-V shared 11 different CTX genotypes (A through K). Antimicrobial resistance patterns of the strains varied independently of their ribotypes and CTX genotypes. Results of this study suggest that V. cholerae O139 is undergoing rapid genetic changes leading to the origination of new variants, and temporal changes in antimicrobial resistance patterns may be contributing to the selection of different variants.